NT and 2k pro is 4gb, but divides it up so its not toally useable. NT enterprise and 2k advanced server help some (by splitting it in other ways than 2GB-2GB, I think it does 3GB-1GB) and I think that 2k Advanced Server maxes at 8GB or 16GB depending on motherboard architecture (they must be specially made).
win9x(ME) ONLY USES ONE CPU, don't listen to 00astroguy00. Also with winNT/2k to use above 4 cpus you must again have specially made motherboards.
Pretty much you need to go get on technet and read for a while.