Hmm, I have Poser 7 running on Vista Ultimate 64 with no issues to report!!
Have you set all security correctly, running as Admin etc. etc.???
One thing that does lock Poser or any other prog, but particularly Poser is if some of your folders don't have correct permissions set!

This was a bug in early versions of Vista where you could run as admin but folders still didn't have correct permissions, it's been corrected now with windows updates, so if you haven't run auto updates I suggest you do now and check those folder permissions!

Injustice will be avenged.
Cofiwch Dryweryn.