Once My keyboard was not working properly.so unable to boot in safe mode because of my F8 key was damaged.I found following methods to use on such a time.I have mentioned it for windows Vista and also in Windows Xp.
Boot In Safe Mode Via msconfig
For Vista
First boot your PC in normal mode and go Start --> Run, and type msconfig now press Enter, It will take you to the MS Configuration window.
Click the Boot tab in window and select the check box Safe boot
Make sure that minimal is selected and click Apply and OK.
Restart...
