Profiles

Have you scanned for malware (virus, trojan, etc.)? Are these PCs connected via network, and then to the internet?
Usually Windows doesn't mess up the user profiles much unless one gets corrupted...this is a possibility if all the units are running the same sort of software, like a database or some such. You can tell if Windows is creating a user profile due to corruption by looking at the user name of the created profile. For example,the computer is named CompanyPC1 & the normal user is John, but C:\Documents and Settings\Users\John has become corrupt, upon subsequent boot Windows will create the user named CompanyPC1.John (complete with period) and folder C:\Documents and Settings\Users\CompanyPC1.John\.
First though, run a malware scan on all PCs connected to the network. If clean, check for a commonality, some software that each is running.