My Thinkpad A20m had working acceleration with an 8MB ATI Rage Mobility M1. I remember getting a 3DMark2000 score with it, maybe around 1000 or so. It also ran Ultima 9 in low settings but it wasn't reliable. I only tested it in the starting area. If I put too much of the world into view, I'd get a crash with some message that sounded to me like it didn't have enough video memory.
I never used it to actually play anything, but it probably would have worked with late 90s games.
I think I ran an OpenGL screensaver on it, and I know I did a little OpenGL programming on it, but not much.
At some point, it's 3D capability was broken in IBM's later drivers, and older drivers were removed from their site. It won't run 3DMark2000 anymore. Don't remember if I tried a real game since then. It was never a gaming machine anyway, but I still found that annoying.
My brother had a slightly later Thinkpad with a 16MB Savage Something, which was superior for 3D, but it's driver sometimes BSODed. I never had that problem with the ATI.