Well actually, it makes up an awful lot for not having such a good graphics card! It doesn't utilize the full force of the four cores but it certainly shares the work-load across them and enhances things a lot!
Certain systems can utilise many cores. OSX supports god knows how many now, XP isn't so hot with them but I hear Vista supports dual core (for the OS themselves). Crysis supports a max of either 8 or 16 cores. Most AAA rated new games at least support dual core.
TBH, never go with AMD, for the second you will - intel will bring out a chip 1000x better, along with 8 more cpu's to choose from in that series, most likely.
AMD are cheap and cheerful and aren't as good at Intel. They once had the upper hand for about 6 months and business was booming for them - but that time has since long passed and Intel simply wipe the floor with them now...
If you're on a very tight budget then go AMD, otherwise, save a little bit longer and get an Intel.