Note that doing so is technically a violation of the DMCA (a stupid law, but a law nevertheless). Using the sony-supplied removal tool (assuming you can jump through the hoops to get them to send it to you) is even worse, since the Active-X control required in the process opens up your machine to arbitrary software execution from any web site you visit from that point forward.
Legally, the only way to remove the rootkit is to reformat your hard drive and reinstall the operating system from scratch. On the other hand, if this software (Sony's rootkit) had been written by an individual or small company, the authors would be in jail by now. If Sony is above the rule of law (and it would appear that they are), then should the law (even bad law like the DMCA) be part of their arsenal?
Can't you use Tools->Manage Add-ons... to disable it after use?
-PJ
I'd love to see some tool-of-the-RIAA hack US Attorney take someone to court for violating the DMCA over removing this rootkit from their PC. If I were defense counsel I'd make sure the case was heard by a jury composed entirely of Windows users who had spent hours upon hours removing viruses, trojans, worms, spyware and spam from their machines, had to wipe and restore their hard drives from scratch because their OSs had become hopelessly corrupted by all that crap, and had lost irreplaceable data as a result. I could prtobably find such a jry in say, about five minutes or so. By the time I had finished with them, not only would my client walk out a hero to the computing public, that jury would be ready to string up the attorney and his coked-out complainants.