If matched with a gig of RAM and a 6600 GT, would the AMD Sempron 64 3000 have enough power to smoothly run HL2 & BF2 on medium settings and 1024 X 754 or thereabouts resolution?
Yes that processor is just fine. However you might need another gig of ram b/c it could get a little choppy in crowded spots in BF2.
The 1Gb of ram will be fine for HL2 and CSS, but not BF2
I'm disagreeing on the 2 gigs of ram thing. That sounds like, way, way overkill. A gig is about right, and maybe a 1536 mb of ram would suffice. 2 is expensive, and overkill.
1.0 gig is not enough to run BF2 on high smoothly. 1.5 gigs is Ideal for running BF2 smoothly. 2.0 gigs is perfect and will run BF2 on max at any resolution.