This registry edit creates a new "hidden" user account. To log on using the account it's necessary to use the Log On To Windows dialog box similar to the one in Windows 2000.
[Start] [Run] [Regedit]
Registry Key: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\WindowsNT\CurrentVersion\
Winlogon\SpecialAccounts\UserList
Make a new Dword Value
Value Name: HiddenUserAccountName
Value Data: 0
Exit Registry and Reboot
The account will be hidden on the Welcome screen, however the account profile will be visible in C:\Documents and Settings (default) or wherever user profiles are stored on your system as well as in Local Users and Groups (in Computer Management).
Yes this is the same thing that strasharo just posted, but his must be run from a batch file. This may be done yourself. Same effect.