I've been thinking of trying Linux on an old laptop I've got, the thing is it doesn't have an internat CD drive and I don't think it can boot from USB.
If it's that old, don't try using Ubuntu or one of the mainstream distros - it'll crawl and you'll struggle. Like MR said Puppy or one of the other lightweight distros are geared towards getting the best out of older/low spec hardware.
Oh and Ben they sorted out the wireless in Ubuntu some time ago - I recently set up a PC for the kids using a tailored kids' distro based on Xubuntu and it runs wireless fine (well except for the normal problems I get with wireless - apparently the Victorians built labourers' cottages with walls thick enough to withstand small tactical nuclear wars)