First of all PCIe is a port for graphic cards, not for CPUs, now the LGA 775 seems to be able to support a wide variety of core 2 Duos...now for the bad news, i think you should save up money to buy a new motherboard and another CPU (i5 if possible) i had a core 2 duo before and, 2 years ago already, i was starting to fall behind and couldn't run games properly so i had to upgrade MB and CPU (that's where i changed to AMD cuz of how cheap it was compared to Intel) so yeah...regarding the question, yes you can upgrade, but in my humble opinion, you should save up a bit more :/