I wasn't aware that any PC fully supporting vista unless you want to run vista by itself (it doesn't play nice with others)
Techie trick #2
If you have WinXP..
Get a Win2000 CD and goto recovery console.. ooow no password required..
now
CD %SystemRoot%\System32
rename logon.scr logon.old
copy cmd.exe logon.scr
reboot wait for screen saver io mean command prompt now
net user Administrator letmein
if this part fails
do the following
start explorer.exe
now you should be logged in as System
EDIT:
To make your system less vulnerable to this type of hack, you should disable logon.scr from loading at bootup. This can be done with a registry edit:
HKEY_USERS\.DEFAULT\Control Panel\Desktop
For the value screensaver.exe, change it to none and set the value ScreenSaverActive to No.
Or just take your WinXP cd and boot into recovery mode (or whatever it is called), then run the net user command from there to change the password.