I've got the original xbox version of this game but unfortunately can no longer play it because it doesn't work on the xbox 360.

I never got round to completing the game because while I was playing it I traded in my original xbox for a 360 thinking I could use the game on that.
Unless MS update the emulator so that this game works which is unlikely then i'll never complete it unless I get the PC version.

Are there any demos for the PC version of the game so I can see if it works on my laptop before spending money on it?

Yes!

http://download.cnet.com/ARX-Fatalis-updated-demo/3000-7536_4-10229016.html

Thanks, Downloading it now

I'm guessing it is only available on pc?

Yes unfortunately.

It's 10 bucks or so on steam, and should run on pretty much any PC....

it was ￡1.50 the other day on steam, so probably about 3 bucks or something for you guys. a deal you cant refuse...