kismets already done, and there is a WEP tool floating around here. It's just that an average collie only has 2 hours battery life, using wifi this drops to about 40 mins. And when you have to collect 20 minutes or so of packets for the cracking tool that doesn't leave much battery life for the actual cracking.
I think I read somewhere that a C-860 had cracked a 128 bit key after like 6 hours. So a collie would likely take longer with its slower processor.