I took out a hard drive out of my step dads computer and used a enclosure and put it on a new one read on ....?

Hi everyone. I just put a hard drive into an enclosure and I am using windows vista. My step fathers computer was xp and he had turbo tax 2006 on it and I am trying to open it on vista and not having any success doing so. How can I make it so he can view the doents he was working on in his xp computer I cannot figure this out I am not computer illiterate but I am having diffuculties can anybody help? Thanks