Yup, it was the card. I was hoping it would be a software thing, but it failed the same way on my sister's machine. It doesn't trash until it's been up for a couple of minutes, so I think resetting the heatsink might do the trick... but I won't be holding my breath...
This is
the card, btw. But even with the one on the mobo, performance on Xfree86 is better than it ever was on Win, Linux brought faith on computers back to my soul!