Disabled a start up process now I cannot log in

I have a Dell Mobile Workstation with Windows XP loaded on it. I got a virus on it about 3 weeks ago. It put a large red screen on as the background and then said I needed to download anti-virus software. I already had Norton Anti Virus on but it did not catch it. I ran a full scan but it did not get rid of it. The program kept putting new windows up saying it had found problems and I needed to download. I did not download but I did try to get rid of it. Since I had Norton System works and it seemed that there was a startup file that was getting started I decided to shutdown some of my startup files that I did not recognize. Well that became a real problem!!

I now have a computer that can go from the Startup/Sign In screen - but when I try to sign in all I get is my background (our dog) and then a flash of the pop up that says Windows shutting down, and then saving settings.

I have tried everything that I could think of but it has not worked.
Things tried -

1. Log in using last known good setting- same as above
2. Safe mode - does not recognize my user name or password (may be related to the fact that the computer was originally set up as a network computer)
3. Safe mode with network - does not work
4. Use original windows disks to try to repair installation - it asks me for the administrator password and I cannot remember it.

Is there anything I can do?

HELP!!!

 

Can I get into regedit?

Is there any way to get to a command prompt and restart the start up process so that I can get beyond the point that I do now and try to clean the system?

 

Windows XP Recovery Console
The parts about Disable and Enable in the above link may interest you.