IMPORTANT read recent posts before doing these steps!
After searching the forums for a bit I found a fix!
1. Place and rename the MSU file in an easily accessible place, e.g. C:\8preview\preview.msu
2. open command prompt in administrator mode.
3. Type: Expand –F:* c:\8preview\preview.msu C:\8preview\
4. Type: DISM.exe /Online /Add-Package /PackagePath:c:\8preview\Windows8-RT-KB2849636-x64.cab
From Johan Rensenbrink on anwers.microsoft.com
So now for the install …
And the anti-climax:
Wow I never thought this would be so hard….