Category Annoyances: after installation of .Net framework the XP login screen returns.
To get rid of it do the following:
Right-click My computer, Manage, Local Users and Groups, Users.
In the right window pane there is a list of all the users on your computer. Just disable the accounts that were added by the Microsoft.net framework update (ASPNET). Close the window, reboot, and the "Select User" logon screen will no longer appear.