I'm have the same problem as u two mentioned... Both machine..... 1. PII 400 Mhz Dual with Radeon R100 64MB DDR 2. PIII 1.13Ghz with Radeon Mobility... have the exactly same problem..... happen.
Both machine using custom-built kernel 2.4.21pre4. while the old version of Xfree86 4.2.1-3 have no problem... after I upgrade 4.2.1-5 both machine not working with 3D anymore..