Go check out BattleScooters, seriously. I posted a link about a ride a kid took from CA to AK on a Moped. It's called "Crappy Little Dreams" and is a great read.
If he can do it on a Moped you can do it on any bike. There's a group of riders fantasising about doing a big trip on TW200s, check out Loisontheloose she did Alaska to Argentina on a XT225.