hope you dont mind another jump into this, rockster asked me to take a look.
for the most efficient cleaning of internet temp files, plus lots of other crud, use CLEAN UP!
I'm sure the malware guys know this tool, I got it from the malware forums...its great for reclaiming disk space from some of the clutter that builds up in machines as well.
it sounds like you guys have arrived at my only other thought, which is to check the other machines, one or several of them are probably infected.
perhaps an easier way to test that- if you have zonealarm on each machine, just hit the lock internet on each machine, then unlock each one individually until you find which one is trying to dial out.
if you dont have zonealarm on each machine, power 'em down as noahdfear instructed.