The open drivers aren't really suitable for gaming, especially with the older cards; the hardware is slow by today's standards to begin with, and the performance of the drivers is the final nail for their casket. They might be fast enough with fglrx to run older games and some new, non-demanding ones, but with the open drivers it's not even funny.
The games I have been able to run "well" on a small 200M w/ radeon are Temple of Elemental Evil, Baldur's Gate 2, Icewind Dale, Fallout, and the Age of Decadence demo. Low resolution, with the lowest graphical settings. Of course, programs detect the chip as a 8600gts card , but other than that I get no big problems.