Leticron

To be honest, jamiemac....I didn't try it out...it was just a "shot from the hip" since, even if it doesn't work, you can't mess anything up that way.
Under Xp there used to be an "Shell=" entry in the Boot.ini but under Vista the mechanics have changed, so I guess there is no avoiding Regedit (which I always try to avoid as long as I'm not sure that I deals with experienced users)
That's why all the alternative shells like Litestep, Aston etc have so called shell switcher programs which simply changes that entry for you ;)

BTW: I believe, under VISTA it's the following entry:

HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\winlogon\Shell = explorer.exe

Just check an see if that if that entry is still there and MOST IMPORTANT, that the value of "Shell" is ONLY "explorer.exe" without any switches or parameters (that might well be a worm/virus)

-le