This will make you laugh:
Mobo: Asus A8N-SLI Premium
CPU: AMD Athlon 64 3700+
RAM: 1GB DDR - 400 (LOL!!!)
VGA: XFX Geforce 6600 GTX
Mouse: Razor Diamond Back
Audio: On-board
System HDD: Western Digital Raptor 10K rpm 36GB
Data HDD: Western Digital Blue 500GB
OS: Win XP SP3
I still manage to get about 100 fps on the stress test running at 1400x900, 2x anti-aliasing, full HDR and most other settings at high.
Total cack for anything more recent than CSS though! Can't afford a new rig this year (getting married - argh!) but I think I'm going to up the RAM to 4GB, get a new video card and whack Win 7 on it. Should give me another couple of years.
I've also got a laptop but I can't remember the exact specs. It's an AMD dual core with 4GB RAM and it's actually got quite a bit of oomph but the VGA really lets it down with shared memory, so I get 18 fps on the stress test and average 28 fps when playing CSS. I can get it up to 65 fps on texture city but only if I stand on the roof and look at the sky
