problem accelerating X server
 

I'm using the SiS 6303 server, and when playing flash movies, when there are large screen areas animating, there's a big slowdown.
The I'm using kernel 2.4.20 (SuSE 8.2) with a pared down twm window manager just running Mozilla.
The machine is a PIII 600 with 128MB (16MB shared for the onboard graphics chip)
The same movie on the same machine running Win2K is fine.
Any ideas if this performance can be improved?