As far as far cry and painkiller yes. If you are talking about the "stolen leaked executable" of Doom III then that discussion is not permitted. If you are talking about the upcoming demo then I would imagine you could, but nobody has played it so your guess is as good as mine.
Your computer ought to play D3 at almost-high settings. Your 9600xt has the horsepower to enable all the fancy effects, obviously without AA or AF and while using lower-ish resolutions. I'd figure that your system could do D3 at 1024x768 at better than 30fps with at least medium game settings if not more...
You really only need UBER hardware if you want to play at high settings along with high resolutions AND high refresh rates. If you're ok with 1024x768 at ~30fps, then your rig should be just fine.
I think he would be able to run Doom 3 with x2AA and 1024x768 above 30FPS.
Anything else in 1280x1024 should run above 30fps, but not in AA and perhaps dip down below that with high action scenes. That 9600XT is not as whimpy as you think... some of its highspeeds with some overclocking can make up for some of its lacking pipelines when compared to the 9500np, 97xx and 98xx series... (not including SE "chopped" versions here)
Your rig is better than mine, and I play the above games at absolute high settings cept Doom 3 of course. I advise you get at least a gig of ram though. Far Cry stutters with only 512mb. What great about Painkiller is that it's so damn pretty and yet runs so damn good.