XP reboot after bad utility registry edit

HI all MG fans,
Thought instead of a boring Hello in the Welcome center, I'd get right down to revealing my continuing ignorance of computer operation, including failure to learn from lessons past:
After trying yet another Clean-up/Speed-up utility (this one's Uniblue's SpyEraser), the final registry "clean-up" resulted in a hard XP crash with a black DOS screen "disk read" error followed by a prompt to reboot using Cntrl-Alt-Del.
The C-A-D results in sometimes getting to the 1st XP boot screen for about 0.05 secs, followed by a return to the original DOS message (mostly I don't even get that far). When I tried to reboot using the XP CD setup, the repair option copies all the setup files very well, but XP crashes back to above screen on reboot.
One option I couldn't try involved a prompt to type in my Admin password, which is my 1st question: 1> Since this XP is a reinstalled OS using a new OEM XP CD (bought new from Egghead), I never created or needed to use an Admin password before, and now the box has 3 Users, lots of data, no full system backup, and I Really don't want to reinstall it again. Is there a default password I could try (pushing Enter on a blank space doesn't work), or some other way to finesse the Admin password block?
I just need to get back into Windows so I can use System Restore and get on with life, if you get my meaning.
Any suggestions will be gratefully received, and the 1st one that works will receive a surprise visit from my fairy godfather

 

quote, I just need to get back into Windows so I can use System Restore and get on with life, if you get my meaning.

Im not sure thats going to happen, how did you get windows installed on the first try? ed

 

On 1st try, I installed XP from a new OEM CD on a new C drive, no problem. We wound up with 3 Users, each with his own password, all administrators by default, no limited Users. The system gradually became unstable, seemingly because of software conflicts but not due to virus problems, at least according to clean, updated virus scans. We decided to reinstall XP again from the same CD, this time without passwords, and tried to be careful about reinstalling programs over the past 6 months. System seemed OK until the latest conflict was with an uninstall of HP All-in-One software, which never worked right despite several round trips with the software downloaded from HP. I installed the Uniblue utility to get rid of the last of the HP files, which refused to go away even after Add/Remove and HP's own Uninstall left 30+ files still there.
Does that help clarify things? Any help with XP password defaults, workarounds, etc?