Vista - Assassins creed problem

Hi, I recently fired up assassins creed. I can only seem to play in window using directx 10. When I use Alt+enter the game freezes (or i just get black screen and have to ctr+alt+delete and close process to get out).

I did get it to work once but I cannot seem to replicate it.

When I use the directx 9 .exe start it automatically uses full screen (but I noticed quality is not as good in opening scenes, has slight glitchy lines like a weak static effect).

On a side note I notice that forums mention directx 10.1 ...how do i check what version of directx I have? I have the latest ati catalyst version 8.12 (is this where I can change what version of directx I run in a game)?