how to extend my wireless network to reach my neighbor’s pc

Hello
I’m having a bit of trouble recently. My neighbor wants to share my high speed internet connection over my wireless network but I don’t know how to achieve that.
I have my XP pc plugged into my router (DLink WRT54G) in my office and my Vista laptop in the living-room accesses the internet remotely via the router. Now I want to offer my DSL to my neighbor (2 buildings from me, on the same floor) but I don’t think it’s possible right now. What do I have to install, change … to make it so? Please I really need your help and expertise. Thanks in advance