and then save it as a .bat file, for example x.bat not .txt. Then double click on the files you just saved and it should execute some commands that should replace your screensaver with the task manager. Now logoff your limited acount and wait for 10 to 15 mins, without touching the mouse or keyboard and wait for the screensaver to come on, which shall be the task manager. When it appears click on New Task and in the box type in regedit. This should open up the registry editor. Now go to the hive HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon and double click on AutoAdminLogon and set the value to 1 and click ok. Now refresh the registry and close it, and then restart the pc. Once the pc is restarted you should automatically logon as Administrator.
Now you must put your screensaver back to normal by opening notepad.exe and by typing the following:
I've used a product called ERD Commander produced by Winternals. This is a proper Disaster Recovery program. You boot from the disk. When the Command Prompt appears, one of the features is the ability to change any password on the machine including the Administrator password.
I've just checked their website and it looks like they are now doing a free version. You can find this here: Winternals
Hopefully this will help.
[Edit] Sorry, doesn't look like it's free after all. But I know that this does work as I've used it in the past. If you have physical access to a Windows machine, it isn't secure with this product. [End Edit]