I have no idea. Use dism.exe /online /enable-feature /featurename:NetFX3 /Source:d:\sources\sxs /LimitAccess (put it in the setupcomplete.cmd and first detect which drive is the DVD drive) to install NetFx3
setting the XP compatibility causes an UAC prompt, so the messenger runs elevated. This is not good. A better way is to use ACT and only set the XPSp3VersionLie.
The CPU is high casued my spikes of the sidebar.exe and the WMI service. So it looks like a gadgets queries some data (network data like IP). So stop some gadgets and look if this fixes your issues.
Btw, it is possible to fix the "connect to network" dialog and bring the Win7 version back? I hate when Win8 fill so much space which this dialog. (source: xpclients topic: )
Try to generate a crashdump of the MMC.exe: http://msdn.microsoft.com/en-us/library/windows/desktop/bb787181%28v=vs.85%29.aspx open it in WinDbg and look at the callstack. Do you see why it crashes?
C:\Users\Andre>err 0x80040155 # for hex 0x80040155 / decimal -2147221163 : REGDB_E_IIDNOTREG winerror.h # Interface not registered # 1 matches found for "0x80040155" try to register the DLLs with regsvr32.exe.