stuck upgrading screen

I downloaded the 32 bit version of Vista and im upgrading from service pack 2. It copies and expands the files just fine however when it reboots it gets stuck on the pretty installation screen saying "updating windows" or something similar to that. I can move the mouse cursor around as much as i like during this stage. I went to work and came back 4 hours later and there was just a black screen with a flashing text marker " _ " like in DOS up the top left of the screen.
This screen was unresponsive so i restarted and it went to a sceen with two options....one of which was Setup Rollback or something like that which it selected almost instantly. It removed what had been installed and here i am.
Any thoughts on it? Could it be a bad download or possibly a bad burn? I'll re-download it tonight but it doesn't feel like one of those problems
Also my computer is well above all the specs required to run vista.
Cheers in advance!