I needed to have my tv account automatically logon on startup (for obvious media centre fun). Microsoft has a nice KB on how to do it:

http://www.microsoft.com/windowsxp/using/setup/learnmore/tips/knox2.mspx

In case they delete the article you just need to go Start > Run: control userpasswords2 [Enter key]

Then untick the 'require password to logon' and give credentials for the account for default logon. Easy!