Trouble getting rid of one last bad thing...

Okay, I've done all the stuff in the "Read me first..." thread and cleaned a ton of crap off this computer. Everything appears to be clean, but on every third or fourth reboot, something tries to install either Search3 Search Bar or IBIS Toolbar (seems to be random). I say "something" because I cannot locate it in the Hijackthis logs and scans with MS anti-spyware, Spybot, Ad-aware, ewido and Norton 2005 all come up clean. None of the detection tools find anything when I scan, yet when I log into one of the four accounts, it occassionally tries to install one of those two pieces of malware. MS Anti-spyware always catches it and disenfects the computer, but subsequet scans (with all the tools listed above) say the computer is clean. Bottom line, what the heck is hiding on this computer trying to install those malware components? Any ideas? I have less than 24 hours before the computer goes back to it's normal owner (the one who infected it in the first place), so I'd love to get this one last thing cleaned off...

I am attaching a zip file with HijackThis log files for all four accounts on the computer (not counting the Administrator account since it is never used). They all appear clean, but if someone can catch something, I'd greatly appreciate it...