Hey, JW. Please click the User CP link and complete your BW profile re: vehicle and location as that is often useful information.
Check your manual, you don't need to plug in anywhere to reset the service interval, you do it with the procedure in the manual, key position two and then buttons on the cluster and steering wheel.
That said, if you're in the states you'll have an OBD-II port under the dash and you can use a regular code reader to keep up on things, quite affordable options.
Across the pond that's unlikely, you're limited to the 38 pin connector under the hood. If you have a laptop with a serial port, then hit ebay.uk and order the multiplexer carsoft setup, that will do pretty much anything you'll need for about US$120 or so.
Also, this is the general forum and you have a W210, so come join the rest of us in that forum on this site: W210 E-Class - Benzworld.org - Mercedes Benz Discussion Forum
Lots of great folks, excellent tips, help and DIYs, too. As well as a wealth of specific -- not general -- information.
Take care and enjoy the ride,