I tried to resotre my system after a couple failed installs of OneCare and both times the program files remained afterwards. I don't think most people have dual boot systems but, i found the best way to remove all the files (even protected "access denied" files) is to do it from another partition of windows in safe mode. OneCare proved to be a huge waste of time, at least for me, until they modify their install/uninstall. If anyone is having problems removing some files after a failed install, let me know. I'd be glad to help as i just went through it.
