Hell, no the 7800GT is the way to go. Its SO **** cheap at $320 its unbelieveable...
Wow man, thats a crazy good setup, you've got skills
I also suggest changing the power supply to a more reliable brand (Aspire is all about flashy stuff).
Other than that, if you can afford it, you might want to get overclocking RAM. There are ways to overclock the processor without overclocking the RAM, but overclocked RAM can be a substialtial performance booster.
Also concerning the RAM, to run today's games on highest (and trust me, that system will run them on highest, escept for my next poitn) you will need 2 GB of RAM. 1GB will be fine for mid-end playing, but I suggest upgrading to 2 GB as soon as you can raise the fund for it.
**** nice setup for under $1000 :classic: