Symptoms: No taskmanager, no cmd, no run as administrator, cant install stuff, control panel access (basically you are screwed) and a message keeps popping up that some file is infected followed by a prompt to enter your credit card number and BSOD.
1. Boot into linux (even via live cd), mount your C:\, go to Documents and Settings\All Users\Application Data\
2. Open the exe in Open Office Writer.
3. Cut any string and paste it somewhere else in the file (to keep the same size but change it to prevent it from installing)
4. Boot in windows and voila
5. Additionally (after all this) you can do this: