No, haven't done that yet. It's worth a shot.
In the meantime though, I ran Drive Genius, which initially reported that it could not repair the disk. However on a second try it was able to, then running it again on 'verify' the report was that the disk was okay.
Great! And a restart brought the regular desktop back, everything functioning normally, for a while at least. The most recent other time I'd gotten that far, it only looked good for a couple of minutes before stalling out. I took the opportunity to run TechToolPro, from the original (probably) disk that had come with the computer, and it reported everything fine. Maybe I should have run it earlier, but the general opinion seems to be that Disk Warrior fixes more problems than Drive Genius, which fixes more than TechTool, so I went in that order.
With the computer running normally (at least temporarily) I wanted to de-authorize the computer from iTunes until we get everything resolved. That meant running the 10.6.8 updater, so I downloaded that (it has the latest iTunes which is not compatible with the earlier 10.6 I reinstalled the other day). When I went to check how the download had gone, son reported that the computer had frozen so he turned it off.
So this afternoon I'll try again, and before going for a new drive I'll do that reformat and reinstall. I haven't used Time Machine to restore anything yet; hopefully it will work as advertised.
This afternoon the computer appeared to be functioning normally. However I ran the three diagnostic tools I had: Disk Utility, Drive Genius, and Drive Warrior, at different times, and they kept finding problems. Never the same problem twice, but it was always something. Disk Utility for instance repaired what it said were minor issues, but could not mount the disk. Drive Genius supposedly repaired it, but on the 'scan' function it immediately started finding bad blocks...many of them. Oh, and TechTool initially said the disk appeared okay, but when I set it to 'Surface Scan,' it got up to 4000 errors before I gave up, and it was only 25% of the way through scanning. Sometimes the current desktop would appear on a restart, and always seemed okay, but that's happened multiple times this week, and the problems always resurface. I figured if I could get the computer to pass all the diagnostic tools and then had a successful restart, I'd let it go, but it always failed at least one test.
So I've erased the drive, am reinstalling 10.6 from disk, and will restore files from Time Machine once that's done.
Tomorrow I'm not working so if need be I'll go pick up an HD and go that route.
Finally this past weekend, son and I removed the original HD and replaced it with a new Toshiba 500GB. Installation went smoothly, following directions easily found on the web. Re-installed 10.6 from install disc, ran updater, actually twice as the download was apparently corrupted (first time that's every happened to me), used Time Machine backup to get all his data back...success! It's now been running for three days without issues. I guess I tried every possible thing before resorting to the HD replacement but would have saved considerable time by just going that route to begin with. Heck, one of the repair programs I bought (Disk Warrior) cost nearly double what the new HD did!
For anyone finding this thread...if you are a handy person, you should be able to do this job, and with proper backups, you can get back to where you started easily.