Bought a movie and had the same problem. Also using windows XP. Was able to view movie using these steps:
-right clicked on the movie icon in itunes (movies section)
-left clicked "show in windows explorer"
-in windows explorer, right clicked movie icon
-left clicked open with "Quicktime"
-left clicked play button.
Worked fine then, but not in full-screen mode. Watched it in the player. Also tried the same movie on my Windows 7 laptop. No trouble at all playing it in Windows 7. Hope that helps.