For those of you not technically inclined but still willing to do this despite the risks of the game crashing or doing something wrong, here is a player made patch created by launton over at the Guild of Greeters:
Use at your own risk, this is unsupported by Ubi and well most anyone else
Big thanks to Almlys on this one. Here's your answer -- it's possible it might cause problems/bugs. If you encounter problems because of this discuss them here...
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>If you have the demo, do this, it's simple.
Copy and paste the game.dsc file from the "path_to_the_demo/bin/" to "path_to_the_full_game/bin/"
And now edit that file, and change the "full_screen ( true )" line to "full_screen ( false )"
Also, remove "demo" from the window title.
Seems that is working, but not officially supported.
This file is not present in my full installation, but seems that the game is still reading it.
If you don't have the demo, the game will succesfully start in windowed mode only creating a file called game.dsc in the bin folder where the game is installed with these contents.
full_screen ( false )