It looks like no-one else has had these problems with segfaulting/illegal instructions after using X with the tdfx driver.
Hmm. I also a few days ago had a problem during the middle of using dselect, without running X first. The console font, specifically capital T and capital P, was corrupted and segfaults started happening all over the place. I have a 6500 with 96 MB of RAM and a Voodoo 3. If anyone has overcome such problems, or even heard of them happening, I'd appreciate an e-mail (then again, it may well be that my hardware is fried...) Thanks in advance, Arlie Capps