Just curious as to why all the reinstalls? Problems or upgrades? Curious......
Mine was due to a enforced hardware upgrade... my old 939 socket mobo had a fault, meaning I had to also replace my CPU and RAM because AMD/ASUS 938 socket technology is no longer supported/available here in Oz.
Although Vista repaired itself to run on the new hardware, I was not satisfied with its performance (felt it could have been much better due to improved RAM/CPU speeds) so did a clean install to better utilise the OS and new hardware configuration... and I'm glad I did.
Everything positively zips along now... though I'm still baffled as to why my external drive prevented a complete install, given that it's an identical drive to the one Vista is on. I first thought that it may have been due to the data stored on it, but being that's backed up skins, wallpapers, documents and emails, I now have to doubt that theory... the drive is plugged in again and the data has been restored to Vista C:/, and there are no issues to speak of.