I had the same problem... IIRC, installing .NET 1.1 creates another "invisible" profile, ASP.NET, and so Windows no longer bypasses the Welcome screen.
I think the solution was:
Start -> Run -> control userpasswords2
Uncheck "Users must enter a user name and password".
I think you're then asked which user, if any, should be automatically logged on at startup. Type your user name (no drop-down box?) - don't accept the default, "Administrator", even if you are the administrator. This is another "invisible" profile (and in my case, one which had never been used - took me a while to figure out why my desktop had changed and Windows was asking me to take the tour again...).