well this is a very difficult time to decide on PCI express

atm it shows no substantial gain in performance vs AGP 8x

so i'd suggestt if u really want to upgrade then go in for a AMD athlon 64
3000+ and a MSI K8N NEO2 Platinum motherboard

add to it 512mb to 1gb RAM and get a ATi Radeon 9600 w256mb GFX card
and ur loaded to run ALL the GAMES in decent quality

and this wont even cost u a BOMB
and the icing on the cake is the 64 bit tag

it's always good to flaunt a PC with 64 bits

thats all i have to say