I've done some research on the symptoms the PC is displaying. The most obvious issue is that every few minutes, it opens an IE window and tries to visit either one or the other of two allegedly anti-virus sites. Seems that these sites will SELL you software that's supposed to rid you of the infection.
Can you say "extortion"? As if I'd trust these expletive-omitted vermin to write clean anti-virus software that didn't leave any back-door software behind.
Unfortunately, we might have to reformat to get rid of this thing. The tech support sites that discuss this particular infection seriously put that forth as an option, as this virus invites lots of other malware to come on board. The PC was infected from sometime Thursday through Friday morning when I noticed something wrong. God knows what was brought onto the machine in all those hours. But the virus is recently-created enough that not all anti-virus definitions recognize it. Ours is current, and even so, it can't find this problem.