Well first off, i really wouldn't suggest 2008, 2003 seems alot better (in my opinion).
But IP's have nothing to do with how many people can Login. You can only have 2 People simultaneously logged in with windows server standard, and 3 with enterprise. Read this for more information, it is practically like the same thing you are asking:

http://www.besthostingforums.com/sho...hlight=windows

It will hopefully explain more and answer your questions.