@Andreas Schnellbacher - although not what John needs as far as I understand him correctly, changing boot drive letter is not impossible. Find/replace all f.i. C:\ to X:\ in config.sys and the two ini files will do most of the job (carefully checking every occurrence is mandatory). Find/replace recursively in *.cmd files maybe necessary too. Of course without using the WPS for any copying. Not something I would suggest anyone else but doable.
Hi Andi, that's why I wrote near to impossible. It's more work to move the old installation to another drive letter than to start from a re-installed boot drive. Daniela Engert explained the option how to move the installation, but copying has to be made with the WPS then. Most WPS objects refer to file objects from the boot drive. They might lose their link if you change boot drive letters and perform the copy without the WPS.
Even the both ini files contain several places with hard-coded drive letters. If you keep the drive letters of your Apps drive, then the objects keep working. Otherwise you have to adjust countless config files, e.g. those for Mozilla apps, manually.
After all, I seem to have misunderstood John a bit.