ya, i delt with this with diong an update. HEres the problem, atleast for me.
UNPLUG your dvd burner or cd burner. Thats what the problem is. Atleast then
u will be able to get into vista but you wont be able to use any cd/dvd
burner internal or external. Pretty mcuh your screwed, the only way really to
deal with this is to do a fresh install of vista. When you do a fresh
install, leave the cd/dvd burner unplugged until you get the windows fully
installed. THen plug it in after everythign is done.

I tell ya, i had the same exact problem with ultimate. I dotn know why tho,
my brohter got it for his laptop and the upgrade ran fine. So, unless anyone
else has ideas how to do this, all i can tell ya is do a full install or just
go without a dvd burner