Apevia PSUs are not reliable with my past experiences. Alot of the PSUs they supply die withint 6-10 months of use. Ive experienced it with a few servers ive owned in my past. Rosewill, antec, hiper are my recommondations. From your setup above, I give it about a 7. Now days if your a gamer, Usually youll have a game, a browser, maybe music or some kind of programs. Usually if I run World of warcraft, Ventrilo and Mozilla Firefox it uses about 50% of my system memory. I have 2 Gigs of ram in my rig so if you have 1 gig itll just about use all of your system memory. Just depends on what you have open and such. As for the video card the 7900GTO Outperforms the 7950. But yeah, Trash the apevia PSU. Get a Rosewill, Antec, or a Hiper. There all good.
Aspire X-Navigator Series
Intel 3.66 Ghz Dual Core
2x 1GB Kingston 4-4-4-12 Ram
ECS P4M890T-M2 LGA 775 M/B
Nvidia Geforce 7900GTO 512 MB PCI x16
Rosewill 700W PSU
Seagate Barracuda 250GB 16MB 3.0gb/s