The difference is that the number of pixel processing pipes is halved to 4 in the 9500 non-pro, instead of 8 in the 9500 PRO. Also, the clock and memory frequencies may be a bit lower I believe.
The number of pipes is limited in software drivers however, and not on the actual GPU, which is architecturally identical to the Radeon 9500 PRO and 9700.
Many users have had success increasing the pipes back to 8 with a special software driver. You can learn more about it on the forums at rage3d.com
The bottom line: You're definitely better off with the 9500 if you're into modding and overclocking.
If not, it's a bit of a closer race, but the vanilla 9500 non-pro will still kick the pants off a 4200 when using AA and anistropic filtering.
Be well,
- Cleeve
<P ID="edit"><FONT SIZE=-1><EM>Edited by Cleeve on 03/10/03 12:32 PM.</EM></FONT></P>