If you have the space, Install Windows to another directory (best if to a different drive, but not necessary) during the install, and boot that to copy files around to fix your existing and primary windows installation. Then adjust boot.ini to have an "Emergency Repair" boot option, and you can always boot into this installation to fix your real installation. Just be extremely careful to watch for the signs of a dying drive - if it's dying, you need to switch to "copy the stuff I need off to a different drive" mode. I assume it's not backed up, only because I've yet to work on a system that's not my own that was... and remember - the fact that a file went unexpectedly missing during the install is strike one and two already that the drive might be going toes up...
Or one better (if you have a little Linux experience and can know enough to mount a partition and copy files) use a copy of the Fedora 9 Live CD - and Live boot Linux to copy the files you need around on the Windows installation. This has become my favorite method of fixing the friends/coworker's thrashed laptop that doesn't ever have a floppy drive any more - 90% of the time you can't install Windows other than via the "Recovery CD" that typically wipes the drive because it requires special drivers - and half the time you are fumbling around in the dark trying to determine exactly which drivers you need to Slipstream, which is time consuming to begin with even if you know exactly what you need. And any time you try to do a bunch of writing to an "iffy" drive you risk destroying what else is on it but good.
Amazingly, I've not yet run into a laptop that I couldn't at least boot Linux on well enough to copy files - even though the Windows installer itself boots only about 1 in 5 these days.
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