What are you looking to play on it?
Couple of issues:
1) You're restricted to 4GB of DDR2 @ 1066 (1333 if you kind some ddr2 that is compatible, but its still a 32bit OS)
2) You're restricted to SATA. Slower transfer rates.
3) You're restricted to the previous generation of Intel CPUs. You can buy some quad cores in the old Yorkfield architecture, but against the new sandy bridge architecture, they lose ground.
In so far as GPU compatibility, I'm actually not sure. It looks to me like you drop anything you wanted in there... But don't quote me on that one
My advice would be to buy a new one. Your machine would have been good once upon a time. But tech moves so quick that once you get a little bit behind the ball, you're sunk....