If you can run a coaxial cable all the way from your house to his, then you're set
.
It would be pretty cool though, if you could modify a modem to transmit to your walkie talkie, which would then transmit to his modem, which would then give you net access.... Hmm... I wonder how hard that would be to do. You'd have to find out first if it can be done, but if so, then it might very well work.
But 802.11b would definitely have been the best option. If you could persuade the school to let you attach an antenna to their roof, to act as a signal redirection point, then it might work.