Vista - Vista RC1 install over beta2 multiboot with XP pro - oops, big pro

(very) brief summary:-

XP Pro system (development system), installed Vista beta 2 using multiboot.
Worked perfectly, very nice, played around, reported a couple of bugs.

Installed RC1 over the top of Beta2.

RC1 copied all of Beta2 files into "Windows-Old" directory. Unfortunately it
also copied ALL the boot files required for multiboot, so that stopped
working.
Solution, copy files back and used bcdedit to add the XP boot entry again
(the boot entry was already there so I suspect all I had to do was copy the
XP boot files back into the boot drives root folder)

Second problem : somehow RC1 has completely foobared my XP install.
It now takes a long time to boot, the explorer shell had crashed a couple of
times (just by plugging in a USB stick).
Visual Studio 2005 C++ debugging is completely trashed, multiple
unexplanable errors (set document title returns an error, trying to access
memory at 0xcdcdcdcd within CMultiDocTemplate class, and that value is in an
internal member) in the microsoft MFC DLLs. It looks like Vista has copied
some buggy DLLs into the XP system32 directory, OR reset the default app
search paths in the XP registry.