From the Windows Update:
(This is the one that prevents SP2 from installing)
The updates that fail to install are:
Cumulative Security Update for ActivX Killbits for Windows Vista for x64-based Systems (KB978262)
Update to .NET Framework 3.5 Service Pack 1 for the .NET Framework Assistant 1.0 x64 (KB963707)
Any help would be greatly appreciated!