In case of emergency I suggest the following... And yes I know it sucks...
Create an Administrator account
Home Versions - Using command prompt: net user Administrator /active:no (Note: change Administrator to match your created username)
Pro/Ultimate - Using Group Policy: Follow above instructions using GPedit.msc or other
Open regedit, then browse to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System, edit the "dontdisplaylastusername" value from 0 to 1, then export this key as "Enable-Login.reg" somewhere where you will remember it. Edit the value BACK TO 0, then exit.
In case of emergency, you can now boot from any Vista or Windows 7 media, open the repair option, then use command prompt and reg.exe to open the .reg you just created. Once you import that value, reboot, and you will have the domain style login with no username or password pre-entered.
Unfortunately they took away the nice double CTRL+ALT+DEL to get this prompt, and I have been trying to get it going for some time. Just wish they would add this back so it can be used when needed!