Type his login name in and hit ENTER.
If what you say is true and he usally went straight through to the desktop, this should be all there is to it.
regardless of wether or not he joined it to a workgroup, if you have an option below the password field, logon locally to the PC.
If all else fails, I can suggest a product or two to help you out ... but not on here!
Let us know how you go (im hanging around to get an answer on something myself!).