Oldie But Goodie: Privilege Escalation In Windows

Number One:

Replace C:\Windows\system32\sethc.exe with cmd.exe (e.g. by renaming and/or using a repair CD: with the Vista repair CD you can open "notepad" in the command prompt and execute file manipulations from the Open Dialog).

Restart. At the login screen press "Shift" five times (at this point, you can guess what sethc.exe originally did) and a command window with full system privileges will appear. Often used to replace forgotten administrator passwords:

net user administrator *

Of course, booting some sort of live CD or tool might be simpler.

Number Two:

The btwdins.exe method. On systems with the right Bluetooth service executable, you can execute any executable located at C:\Program.exe with LocalSystem rights. More info here.

Number Three:

A.k.a. the famous "at"-method, there was a lot of talk about this back in the day (about a year ago). Basically, the concept went like this:

Open a command prompt as a normal user, type:

at

If it responds with an "Access denied." error, you are out of luck. If it responds with "There are no entries in the list." then you're good.

Now execute:

at 18:15 /interactive "cmd.exe"

And at a quarter past six a command prompt will appear, with SYSTEM privileges. Sounds sensible, right? Not really, since the only users able to schedule commands are already local administrators.