A Windows XP SP3 laptop got stuck during boot with message "umpnpmgr.dll is a bad image" from services.exe. The file seems to be the Plug-n-Play driver. When I renamed the file using safe mode, it would say "couldn't find umpnpmgr.dll" and refused to boot into even safe mode anymore. So I got a hold of an old copy of umpnpmgr.dll from a WinXP SP2 computer and put that on using safe mode (after I renamed the bad copy back). This solved problem.
There's one thing I'm not sure: the booting issue didn't occur right after the installation of SP3. The only thing I can remember between then and now is that I put on a Motorola DCT62xx driver , so I could record stuff off it.