Can I limit user bandwidth/ram usage/CPU usage in Windows 2003/2008/2008 R2?

You can try Windows System Resource Manager. I don't believe you can control bandwidth but you can control CPU and memory usage.

http://www.microsoft.com/windowsserver2003/technologies/management/wsrm/default.mspx

http://technet.microsoft.com/en-us/library/cc771218(WS.10).aspx

For complete bandwidth control you will most likely need to setup a proxy with authentication, and give separate login/password pairs to your users. This way you will control both speed and total traffic consumed per month.

Look for something like Kerio, ISA, Wingate, 3proxy, Freeproxy. Squid could be capable of doing that, too.