As I said, I don't use Shifter. So perhaps, if you don't mind dropping that, you shouldn't be using it either (at this point in time and space).
So uninstall (through Add/Remove Programs):
- Deus Ex Revision Demo
- Shifter (if it's in there)
- Deus Ex
There may still be remnants in the registry, but I won't tell you how to get rid of those.
Now just install Deus Ex from the CD. Do NOT install it to the default directory, but point it somewhere new, somewhere fresh, preferably on a whole different drive or partition on the drive. The installer will make the new directory for you.
Start Deus Ex. Exit it from the intro screen.
Then just only install Deus Ex Revision Demo 1.2 on top of Deus Ex.
Start up Revision with the Revision icon on your desktop. Do Not use the Deus Ex icon.
Set up the game to your likings, start a new game, play a chapter or 8.
And only then, if you truly feel you need to, you can go install Shifter and replay everything.
If, for some reason, Shifter will wreck your Deus Ex/Revision again, you found the culprit. Though then I think you'll have to go to Shifter's makers and complain to them about it.