Thank you everyone who responded to this message. I did successfully replace my alternator (Mercedes calls it a "generator") over the weekend and thought I would share the proceedure to do that. I didn't take pictures but hopefully the step-by-step removal procedure will be helpful for others looking to do this.
I have a 2006 S430 so the following steps refer to this type of car:
1. By a reconditioned alternator. The new ones are ungodly expensive but don't cheap out and buy anything but the Bosch OEM version. Trust me, you won't want to do this more than once so buy a good one. I buy my parts from this online retailer. Quick service and reasonable prices.
Discount Auto Parts Online - Import Auto Parts -- PartsGeek.com
The cost was $284.94 and they charge $111.00 for a core price which you will get back when returning your used one.
1. Remove BOTH the positive and negative battery terminals. The negative first. Not removing both can damage the diodes in the new alternator. The battery is in the trunk on the passenger side below the trunk flooring.
2. Raise the front of the car by placing it on either ramps or jacks. Always err on the safe side and use jack stands when working below the car and not just a jack to support it.
3. Remove the bottom two underbelly engine trays. They are black plastic and used to smooth the airflow under the car at high speed. This is quite easy. There are four screws that hold the back tray and 8 for the larger front tray. NOTE: when finished and re-installing the trays remember not to tighten the screws too tight because Mercedes uses these frame clips that strip quite easily.
4. Remove the radiator fan shroud. Without doing this there is not room to get the old alternator out of the engine bay. This is also not hard. Remove the two small bolts from the upper corners of the fan shroud. There are two clips on the upper edge that need to removed. I just got a very small flat blade screw driver under them and pushed them up. Next remove the electrical plug connection on the driver's side on the fan shroud. There are latches that need to be sqeezed together to unplug it. You will also need to cut the black plastic tie wrap that holds the wiring to the fan shroud. Next and don't forget this one, get under the car and you will see a single cooling line that is connected to the bottom of the frame shroud in two places. Remove the screws from these retaining clips. This shoud leave the fan shroud completely disconnected. Remove it straight up noting the tabs on the bottom and bottom sides that will slide into their mounts when re-installing. I had to wiggle this back and forth just to get the correct orientation to clear the mounting ears from the rest of the engine hardware but it can be done. With this complete you will have all the room you need to work on the front of the engine. NOTE: Mercedes recommends removing the radiator but I do not. I think they do it to prevent damaging the radiator while service is performed. Just remember DO NOT ding your radiator while doing your work and all will be fine.
5. Next step, release the belt tension by applying a 17mm socket wrench on the welded on nut of the belt tensioner. Turn counter clockwise. I have attache a PDF file that shows the location of the tensioner on page one and the 17mm nut on page two. The picture on the first page is of the 6 cylinder engine but for illustrative purposes shows it's relative position. NOTE: life will be much easier if you insert a pin or hex key into the hole provided in the tensioner after turning the 17mm nut and releasing tension. This will hold the tensioner in a relaxed position while you do your work.
6. Remove the top engine cover (the black plastic one with the Mercedes star on it) by pulling up the front edge first and then the back with a slight rotation to your movement. I can't desribe it any better. The plastic cover is held on by spring clips but be careful not to break them.
7. Remove the passenger side black plastic air intake tube. Wiggle it around it will pull off.
8. The next step is not absolutely necessary but will make things a little easier and give you a little more room to access the alternator. Remove the radiator overflow tank (the one where you add antifreeze). This has only one nut at the top. Pull up on the tank firmly. It mounts on the bottom to the windshield fluid tank by two fingers that will pop off as your pull up. Remove the sensor wiring connector on the bottom. It has a latch also. Do not try rotating the sensor at the bottom of the tank just remove the wiring connector plug. Cut the tie wrap that holds the the wiring in place and swing the overflow tank out of the way. There is no need to remove the tank entirely.
9. Now it's time to work on the alternator. Remove the upper and lower bolts that hold the alternator to it's mounting bracket. You will need a hex socket to do so. Here's where it got a little tricky for me but now that I know it's really quite easy. The alternator will need to rotate AWAY from the engine by moving the top of the alternator where the top bolt held it. The bottom of the alternator will be the pivot point. I couldn't move mine and I thouht one or both of the two copper colored inserts that are press fitted into the mounting brackets where keeping it from moving. In fact this was not true. What I ended up doing was using an aluminum pipe that I use as my "cheater" bare to slip over my ratchet wrenches for added torque on hard to move bolts (use aluminum because it's soft enough to not damage most metals) and placed it on the top of the alternator where the top mounting bolt goes through tap the pipe just hard enough with a hammer to rotate the alternator away from the engine and the top mounting bracket. That was the hard part the rest is easy.
10. By swinging the alternator up and down you can wiggle the bottom of the alternator, where it mounts to the bottom position, out of the bottom mounting bracket "fork". I had to use just a very slight pressure applied by a screw driver in between the alternator and mounting bracket while moving the alternator up and down to get just enough pressure to move it out of the bracket.
11. Now with the alternator free remove the electrical connections from the alternator. The main "large" wire bolts to the back. Mine had a plastic "hat" that just pulled of the terminal. Look at your new alternator and you will see the bolt where the plastic hat covers it. The nut is a "Nylock" type that has a plasic insert to keep it from coming loose. You will need to tighten this to 18 Nm when re-installing. The second connection is a plug that has latches also. Be careful not to damage this when pulling it off.
12. Now the alternator is completely disconnected and can be removed towards the front of the car.
13. Place the new alternator in the car and re-connect the electrical connections.
14. Start by placing the bottom mounting point of the alternator in the mounting bracket fork. Insert the bottom mounting bolt and by applying pressure to it move the alternator up and down until the mounting hole aligns. Tighten the bolt just a little to get it threaded.
15. Now rotate the top of the alternator up and into it's upper mounting position. Again push the bolt through the mount until the holes line up.
16. At this point I removed the lower bolt and added some blue Locktite. The blue type is removable. Replace the bolt and tighten until it's snug.
17. Remove the top bolt and add blue Locktite. Replace and tighten. Both bolts should be torqued to 45 Nm.
18. Replace the accessory belt and by turning the 17mm nut on the belt tensioner clockwise to remove the pin holding it in the relaxed position and slowly allow the tensioner to tighten the belt. Be sure the belt aligns with ALL the pulleys.
19. The rest is just reversing the removal proceedure.
IMPORTANT NOTE: Be sure your battery is fully charged before starting your car with the new alternator installed. A discharged battery will damage the rectifier diodes in the alternator by placing an immediate high current load on them and all the work you just did you will need to do again.
I hope this detailed explanation helps everyone.