Well..is it a mile or is it 20-40 meters. Quite a gap in distance there.

Most likely you will not be able to access his router with standard fare equipment. However, there are some rather high gain antennas that you can purchase that will increase your signal, possibly more than enough if you were in the 20-40 meter range. If you're looking to get a mile or more though, your best bet is to try and build a custom antenna (guides throughout the net on that). Some claim they can get signals from MILES away, so these may be an option to shoot for (I havent built one myself yet, but was considering it for a spare time project). People were using everything from pringles cans to old satellite dishes.

However, the BEST option would be to get internet you can game on in your own household. If your friend is really not your friend (someone just has internet nearby) or your friend isn't actually the one PAYING for the net (parents), then you may not even be allowed to hop on their connection. This is a gray area in legal texts, but unless you have permission, I wouldn't do anything but get your own. Besides, dealing with range like that, a LOT can go wrong with your signal, making it more of a headache than it's worth.