As long as the chipset is supported and there are no yellow exclamation points in the device manager, then you should get any ATI HD card for AGP.
There is this one
with 256 bit memory. This is the one I would get out of what is currently available.
Or you can look at this link
If you can find what is in my specs for sale, that's really the one you want. But I don't think you could find that any longer.
As always, pay attention to necessary power requirements of any new card in comparison to your current power supply.