Vista & 7 both have UAC activated by default which can cause problems with installers of all types, the best way to get round UAC (apart from switching it off, not a good idea) is to do what YngPhoenix said, install them to either the desktop or a dummy folder then move the files where you actually want them.

Of course if the installers are actually corrupted that's not going to help in the slightest.

Windows 7 64Bit
Poser Pro 2010 SR1