This has happened to me before.. Like said previously, mup.sys is not the culprit. That is just the last file loaded that you see.. It is another file that is the prob. You NEED the windows installation cd and boot from that. If you have home, then any xp home cd will do it, if you have pro, any windows PRO cd will work.. If you dont have one, borrow one from a friend (hopefully). Then boot from the windows cd. When you get to the first screen, select R for repair. It will open a dos window type /? and it will give you a complete list of functions you can perform. You need to type in this command. chkdsk /r The R indicates that any bad files on your OS will be fixed by the installation cd. It might take hours. For me it would get up to like 75% on step 5 then jump back to 50%. It just takes TIME to fix the errors.. After that I could boot into safe mode ok.
Hope this helps.. but only if you have a windows cd. And make sure your bios is set to boot from CD before booting from Hard Drive.
Good Luck