The helpdesk people at ASUS basically told me to "Buy a non-ati card".

Yeah, they would say that... especially when you consider their graphics partner is Nvidia and not ATI.

I would also try the following :
- Flash the motherboard with the latest bios.
- Try another Radeon 9500 card, but one from a different manufacturer. Also make sure the card is AGP 8x compatible. Some of the earlier ATI cards were AGP 4x I believe.

If that also fails, then you might consider getting rid of that motherboard. If you're not into overclocking, get yourself an Intel motherboard. I now have an Intel board after having used Asus, Aopen, Abit, Gigabyte, Soyo, Shuttle & MSI and can honestly say that this is the most stable board I've EVER had. (Aopen comes second, Asus third). Only downside I can see is that it's not overclockable, but I don't do that anyway.