Your best option would be to use an outdoor wireless bridge. A wireless bridge will connect to his wireless router and also provide you a WIRED connection on your end.

You can then use this wired connection to connect to a hub (to provide multiple wired connections, or connect to another wireless router yourself for your own wireless. Note if you use your own wireless router, you will need to connect the bridge wired connection to your WAN port and manually configure the IP address of your router to be friendly with the IP scheme of your friends.

For example: Friends router IP address = 192.168.1.1. Wireless bridge set to 192.168.1.2. Your router IP address 192.168.5.1 (different) but the default gateway is 192.168.1.1.

For the wireless bridge I recommend the EnGenius EOC-2610. This is an outdoor unit that supports power over ethernet. It puts out 600mW and has a 10dbi antenna for $99.

RFMAN!