[randomness]

Get a motherboard which supports ALL core 2 duo cpus, e.g any P35chipset such as Gigabyte P35-DS3L---this MB should be less than 100$ if u shop around.

Try upping ur RAM speed to DDR2 667...it should not be much more expensive than 533. <40$.

For a graphics card ~100$ is a pretty tough choice. Try to find an 8600GTS or 8600GT if ur budget doesnt extend that far.

160GB HDD's should only be ~50$ so ull b fine in storage.
I suggest trying to save up more money to buy a better comp otherwise ull need so many upgrades in the future.