If it is XP Home Edition, you cannot change the user account name, only the name that is displayed at the Welcome screen.
For any other version:
1. Right-click My Computer, and then click Manage.
2. Click Local Users and Groups to expand it.
3. Click Users.
4. Right-click the account that you want to change, and then click Rename.
5. At a command prompt, run the set
command; the %HomePath% variable still points to the old user name.
This does not change the name of the folder that appears under the Documents and Settings folder for the user.
The other thing you can try is if the display name for a user account has been changed, you can find out which account the new display name belongs to by logging on as that user, starting Task Manager, and then clicking the Users tab. The user account that is marked as active is the one that is currently logged on.
[This message has been edited by IMSA GT (edited 03-16-2011).]