there's a long thread about this if you look for "flying the bike." IMHO the best way to go is a hard case (borrow from your LBS) and check it on the plane. things to know, though:
- airlines can charge you for it, as much as $60 one way. if you lie about the contents, you can usually squeak by without paying, but you might be charged for oversize anyway. (I've been charged just 1 of 8 times I've checked a bike)
- you can check it in a box or hard case. you'll need to remove stem/bars, seatpost, both wheels, pedals.
- shipping it costs ~$40 each way, but can take significantly longer.

me, i've made the switch to S&S couplers. highly recommended.