By George I think I've got it!
Sorry to post again, but I've edited it!
For those still struggling, things I learned along the way.
First, RegDatXP cannot edit keys to be larger than they are set to be. Since the value of the key “UserInit” was reset to nothing with a length of 1, RegDatXP cannot increase it to contain the correct value:
C:\WINDOWS\system32\userinit.exe,
Second, the Load Hive thingy is *scary*. Seriously, you appear to be loading something into your own Registry on your functional machine! But it doesn't seem to hurt anything on your PC's registry. <deep sigh of relief>
Follow Malloc's instructions, click on HKLM hive, Load Hive (use a really unique name so you'll see it - NOT a name like other hives and keys), go to your newly loaded hive, edit the value of UserInit, and then go back to the top of your new hive (I called mine Ed) and Unload the Hive. It saves the updated hive back where you loaded it from, in my case, on my uncle's hard drive.
I'm putting the drive back into his computer... and... it works!!
Somewhere along the line, both my and Uncle's PCs now skip the login screen, but I'll go into control panel and reinstate that. It's certainly a tiny problem compared to the logon/logoff loop!
Can anyone confirm that 1) this was a Spybot problem, and 2) ... I'm not sure - should I update his Spybot, or just tell him never to run it again??
(My problem with Bart was that I used my husband's Bart CD - we didn't realize that Bart CDs are situation specific, and the links that I visited from this thread didn't give instructions - just told you to create a Bart CD.)
Hard drive intact and accessible?
I'm guessing that all my data is still accessible and intact? I'd like to take my pc to a computer repair place (Geek Squad, etc.) and have them image my hard drive and then I'll just throw my dell in the garbage (courtesy of spybot). My time is worth more than the hours I know I'll need to fix this mess that sypbot apparently created with their malicious product. I'm buying a Mac today and will never use spybot again.