suck it up and build a new rig. that mobo is gonna be the big problem. I'm gonna guess your old case might not be able to fit newer long high end cards.
You probably could get a c2q9550 or something on there, (might require bios flashing)...
but yeah 1080p 60fps for 'nextgen' games, would probably cost as much or more to upgrade vs build a new thing.
Nah I used to have an Antec 900 and it can fit most mid ranged cards which could easily replace the 8800 GTS.
f0nz0: If you want that 1080P 60fps and next gen IQ then it's time to replace your old PC. Check the OP for some nice builds, you could try to keep the power supply but you might have to replace it.