@Denique, I am curious but have you installed the patches for the game? I finished playing Assassin's Creed 2 and 1 both on Windows 7 and experienced no issues other than second game having horrible graphics but that is mainly because it was a console port. Things only got better in the game from the Venice level. The in game cut scenes and character face textures were just disgusting to look at. God I hate consoles! They ruin PC gaming in every possible way! Sorry about the rant
I have installed the patches for AC 1, I think! When I started it up this time after a long while, it did a wee patch update thing automatically before the game loaded. I assume that included all the latest stuff.
It's funny you should mention weird character face textures, I've been getting that as well, they all looks a bit blurry.

I really don't know why that happens!
Forgive my ignorance here
digitalrurouni, but what d'you mean by a 'console port'? I've only ever had PCs, so I know nowt about consoles!
My performance issues have gone, and so have the crashing, the problem there was that I had the resolution set too high in an attempt to get rid of the aliasing. Now it's set to 1366 x 768.
I think I might switch to my 1366 x 768 monitor to play the game, rather than the 1920 x 1080 one I'm using at the moment. Will that help the problem of stepping, d'you think?