Change From Domain to Workgroup: Can't Log On

Hello,

I have an account that has a business partner visiting from China. His
computer is running Vista Business (Chinese version). While visiting,
he wanted to access the local file server. He changed network setting
from his domain to the local workgroup. After reboot, he couldn't log
in. My assumption is his computer was never setup with a local
account and the administrator is turned off.

How can I get him back in to his computer? I've tried last known
configuration (I knew it wouldn't work), and safe mode (no
administrator).
When the log on screen comes up, hitting ctl+alt+del does not allow
one to change the user name. This is how I determined the admin and
local user setup had not been turned on and established.

What are my options?

Regards,

Buck