Thanks so much to all of you for your help with this.
After tearing my hair out for weeks, I bit the bullet and turned off the motherboard's Geforce 9400 in the BIOS, and I installed a Radeon 4650 in the PCI Express slot.
I left Vista as my OS, and I installed the current Catalyst 8.12 drivers and the CCC.
I used the CCC to switch to 1920x1080 @ 30i (after loading a different monitor driver to enable that resolution), and then I used Powerstrip to put in Kai's 1080i96 timings.
With some adjustment of the Picture Size and Picture Shift settings on the XG, the new res/refresh worked just fine. It's fairly well converged -- I suppose because my installer had converged a 1080i60 signal in the past.
Then I went ahead and tried do a 120 Hz refresh rate. Surprisingly, it seems to look just as good as the 96 Hz (judging simply from casual watching -- I haven't examined test patterns), and the convergence is actually slightly better than at 96 Hz.
Since I do watch both video-based and film-based materials, it would seem that a 120 Hz refresh rate makes more sense than maintaining separate resolutions for 96 (film) and 60 (video) and having to switch between them.
Can anyone give me any reasons why I shouldn't just stick with the 120 Hz resolution on the XG and be done with it? I've attached a pic of my Powerstrip timings. I basically just worked off of the 96 Hz timings in this thread and then changed the vertical refresh rate, letting the porches, etc. fall where they may. Then I used the XG Picture Size and Shift controls to get the desktop correctly centered on the screen (it was shifted to the left). I'm assuming these timings and my XG manipulations are OK?
Thanks again for all of your advice,