Ive been trying to paste the solution for a while now, but for some reason a website protection warning keeps coming up...
Here is a simplified verion of the answer that hopefully wont upset the web protection software.
Remove quicktime using add and remove programs from the control panel
and then manually remove the quicktime folder from c:\program files\
then remove quicktime*.* from the system 32 directory
Now, re-install quicktime.
ArchiCAD will work perfectly now.