A combo of Windows ME andthe HP isn't too great
But seriously... if you have a virus scan disk or something you can boot from, try that first. If you want to try to put that drive in another system as a secondary drive and get the files from it after that, go for it.
Then, you can still reinstall windows. Go into the BIOS (usually hit DEL when booting), make sure it is set to boot from the CD first. Put the Windows CD in the drive and reboot. The CD will run the setup program so you can either install over the current version or format and start over.
If you need the files on that computer and you can't get them any other way, try installing Windows over itself or in another directory. That's not guaranteed to work though, so beware before trying it. You could lose everything. Even if you get your files, the registry will be wiped so you have to reformat or reinstall all of your programs...