I don't believe it's supported under 64-bit..
It did work on Vista64 before SP1 was released.
Are you trying to install LogonStudio Vista from Stardock Central or Impulse? If Stardock Central then try downloading from Impulse.
I believe it is actually the other way round for this problem. People have been reporting that the version on SDC is currently working with SP1, while the slightly newer version on Impulse will not cooperate with Vista SP1.
Been trying to find the link to the thread discussing this, but can't find it....