A framerate of 15 on an Athlon 3k+/1GB Ram/X1600 @ 10x7 with all settings maxed is actually not that bad.
Yes, I was a bit suprised as well (the demo did set everything to max on default... so I just tried it). The x1600 was my final investment in my old rig, at $100 I couldn't resist. Too bad it's still unplayable, at 15 fps the whole "mouse smoothing" issue becomes more of a "mouse swaying" issue
Anyhow, there's still plenty of games I need to play on the X1600 (I can finally run Riddick @ 60fps, yay!), so I'm afraid Bioshock has to wait for my new system.