I've read this in a comment at digg.com and I thought it was a info worth keeping:

Want to crack WEP? I'll tell you how - Get auditor/backtrack/whax/knoppixSTD/nubuntu whatever security distro you want - run kismet for ten minutes when the network is active - throw the dump file into aircrack - presto. 15 minutes tops for the whole thing, it takes longer to download the security distro than crack wep.

Link to nubuntu. With its 200 megs is a quick download, I hope is as easy as this dude says.