Video cable should be 75 ohm. Audio cable is less than that and if you use it for video then it's possible to get signal reflections which give you ghosting. If you can then buy just normal video cable and run three lots of that just to be safe. If you want to know the details then go here.

One thing tho. You can never have enough wiring in the walls! It's much easier to run the cables now than later. Get them to put a pullstring in as well if you think you'll ever need to add anything.