Why Won't My Mac Connect?

Me and my neighbor share a internet through a wireless router, it's a linksys. He said he'd paid the ISP bill and said he'd leave the wireless router on while he went to europe for school for a month.

Well I got a new macbook while he's been gone and I can't connect to the wireless. I have no idea why. I can connect fine at coffee shops but not to his. I put in the wep and what not, have it set as a 40bit hex. The mac appears to connect but it doesn't seem to get an IP address by looking at my 169 address in system preferances. I can't get into the router's config either because my neighbor didn't give me the password and i checked and it's not a default password. Even weirder, my windows laptop connects fine. It's given an IP via DHCP and every thing and I can browse internet on it. I tried to set a static IP for my macbook and that wouldn't work either. Anyone have a solution?