First of all let me assure you that the Service Release 4 installer doesn't write anywhere else than the directory specified to update. Also, SR 4 does not add or modify any items in the registry (with one exception: the file extensions .pz3 and .pzz are registered with the new poser.exe executable). Yes, the initial version of Poser 5 was protected by InterLok, and yes, InterLok does low-lewel work to protect itself. But, since Service Release 2, InterLok is not used or accessed any more. If you install Poser 5 from the CD and apply SR4 (or SR3 or SR2) rightaway before launching for the first time, InterLok will not even be started and does nothing on your system. To reiterate, when launching after installing SR4, no low-level access takes place at all, the launch process is completely read-only (again with one exception: at the very first launch, a file caching the serial number entered is written to the Poser directory). That said, it is extremely unlikely that Poser 5 with Service Release 4 installed could do any damage to the operating system, and I can't even remotely imagine how such damage should be caused by Poser.