Registry problem

I altered the registry and now Windows will not start. I changed the
following string..
HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices and then I changed \DosDevices\e:
to \DosDevices\c: I got this information from the Microsoft site under the
title "How To Restore the System\Boot Drive Letter in Windows" 223188

I've tried starting in Safe Mode but that won't work and neither will Last
Good Configuration.

When I first bought the machine I had a floppy drive and my removable media
bay and a DVD\CDRW in the fixed bay. The DVD deloped a fault and was
replaced by DEll. they got it wrong and sent the DVD\CDRW for the media bay
at the front. I've since filled the fixed bay with a basic CD ROM drive. I
tell you this because I can't seem to boot from the CD ROM or the DVD CDRW.
I thought if I COULD do that, I could reinstall Windows.

Obviously, I'm dead against a CLEAN install as I have info on the laptop
that I'd like to save.