Deleting primary partition to move to Vista

Hi everyone,
As my title suggests, I'm running Windows XP on my first disc partition, and Windows Vista on my second. I'm finally satisfied with Vista enough to use it permanently, however last time I tried to shrink my XP partition and move my Vista partition on top of that area, Vista would no longer boot until I went into the registry from XP and changed some stuff. My fear, obviously, is that I will have the same problem - and no XP to edit the registry from. Does anyone know if I make Vista the primary (and only) partition on this drive, whether I will be okay? Please let me know, I've been searching for the answer unsuccessfully for so long now!
Thanks,
Ben