I LOVE assassins creed! (got number 2 pre-purchased
I have assassins creed currently installed on my Windows 7 machine at the moment and it runs fine.
your hardware should also be ok to 'run' the game.
I will say though with your hardware, you wont be able to run it at top notch or even high end graphics (shame too cos the game looks awesome maxed out) so you will have to settle for medium to lowish graphics if you dont want to have to your fps below 30.
the game is quite cpu and graphic intensive, which is why they want you to run it with a dual core.