Thanks guys for all your suggestions! The infected PC is being wiped and reloaded - the browser was SO hijacked I couldn't try the bleepingcomputer solution at all. I did forward the fix to our tech support company who will test it.
The key to preventing infections is to block ALL pop-ups - some ask you to click Yes to download antivirus software, and sometimes a pop-up window will appear with no means to close it - this one seems to be embedded in some Yahoo sites - the only recourse is to shut down your PC immediately before it loads. Some folk here who do online gaming using Yahoo have encountered these aggressive pop-ups that load without requiring you to click on anything.
Again:
You guys rock!