Vista won't recognize HDD

I have a dual boot configuration of XP and Vista, with each OS on
their own respective HDD's. I also have a 3rd HDD that has all of my
media documents on it. Through XP, that media drive is linked to [My
Documents]. But when I try to access that drive in Vista, it is
listed as Offline. When I right-click on it in Computer Management,
my only options are Convert to Basic, Properties and Help.

Obviously I don't want to have to change the drive to Basic as I'll
lose my files, but why is it that Vista won't recognize it as being
online when it's Dynamic? Is it because it's already linked to My
Documents through my XP setup?

Anyone know of a solution here that doesn't involve reformatting the
media drive?
Thanks!