first did you install to the program files folder ?  for win 7 thats not a good option because of UAC.

did you right click on the poser.exe file and tell it to run as admin ? I had to do that for vista.

there are some other threads about where to install Poser for vista and Win 7.

Best seems to be to install it outside the program files folder where UAC wont get involved and to set the program rights to be Admin.