OK I figured out BAF and PMC DLC installs on 64bit Win 8. It should be noted that the 4GB limit mentioned above is on and I am running Release Preview now (though both CP and RP had the same error).
You must run the BAF or PMC setup file / Sprocket DLC thing. when / if you hit the error message "Runtime Error".
1. Open the Folder: C:\Users\username\AppData\Local\Temp\BAF
2. for both files "setup.exe" and "ReactorActivate.exe"
3. Right click on each .exe and choose Properties then the Compatibility tab.
4. Check "Run this program as an Admin"
Do the same for C:\Users\username\AppData\Local\Temp\PMC
@a futura memoria