SBS 2003 setup crashes

Hi, I?m the new guy and I need help 🙂

My built-in admin account (SBS 2003) is damaged. My problem is described more or less accurately in http://support.microsoft.com/kb/842469/en-us , but the solution isn?t working for me.
Now, the serious part of the problem is that a 3rd party app. screwed up my Sharepoint, i have to un- and reinstall most components related to it. But, the SBS 2003 setup crashes at “component 19 of 40”,so I can?t. And the setup requires the built-in admin to run, so I?m stuck.

All help (and any reasonable amount of sarcasm :D) would be deeply appreciated.