I only upgraded to Windows 8 earlier this week so I haven't done any real work with Pro Tools yet but I have it installed, it opens fine and plays back my projects fine as well (tried several times including after restarts). Here is what I did for LE 8 I couldn't imagine MP would be any different of a process except the update.
**REMEMBER KILL EVERY APPLICATION POSSIBLE INCLUDING INTERNET CONNECTION AND SECURITY/ANTI-VIRUS ETC THROUGHOUT THE INSTALLS**
Put Pro Tools LE 8 disc in and run the installer, it will give you a few errors but continue on anyway until install is finished and restart once more when everything is complete. **DO NOT RUN PRO TOOLS YET!!!**
Still DO NOT run Pro Tools and now install the 8.0.5 MP update (right click the installer and run as administrator)
http://avid.force.com/pkb/articles/e...675?popup=true
Restart the computer again after install is complete
Again DO NOT run Pro Tools and install the PACE driver update (right click the installer and run as administrator) from PACE
http://www.paceap.com/dldrvr.html
Restart the computer again after install is complete
Now it's time for the first run ***RIGHT CLICK PRO TOOLS LE 8 APPLICATION AND RUN AS ADMINISTRATOR FOR THE FIRST RUN*** remember the first run will take a while :) after you should be good to go.