If setting up a local ad hoc wireless network isn't your cup of tea (...CP/IP), another option for making sure that those functional-but-obsolete computers (and the toxic metals contained within) stay out of the landfill is to make them available to people in poor regions looking to gain new skills. The BBC has a report on Computer Aid International and its latest project, Computers for Schools Kenya. CAI is a UK-based organization that accepts donated working PCs and refurbishes them for use in the developing world (primarily Africa, according to their activity list). They accept donated PCs from individuals and corporations (Mac users need not apply, nor anyone with a PC running anything older than a Pentium II).
While notable and noble, a couple of issues stand out: the first is that, although they mention at the bottom of a specs page that they'll toss in a Linux CD, they strongly emphasize the use of Windows; the second is that sending older PCs to the developing world means that, when they do eventually break, the toxic metals and such become the problem of communities potentially unable to handle the material properly. Computer Aid International really needs to hook up with an electronics recycling service to complete the lifecycle of the equipment they pass along.