Run conduit to all the main rooms, on multiple walls if possible. That way you can run any amount of Cat5 or whatever future cable you want. Failing that, as m

Run conduit to all the main rooms, on multiple walls if possible. That way you can run any amount of Cat5 or whatever future cable you want. Failing that, as much Cat5e/Cat6 as you can afford. There are boxes to convert between every imaginable cable type to Cat5e so you can use them for more than networking if needed.