Rode my XR250 BAJA over a small mountian range to get into Vietnam from Cambodia stashed the bike, then hitched a ride back in a 4x4 back then went through customs on foot. Had a great time riding all over the place Veitnam is a huge place with some of the best beaches I've ever seen, and as long as your NOT American and say that to everyone you meet you will make friends. On a tour of the tunnels our guides didn't talk to the Americans not once, there was real hatred in their eyes.
Thing is dont let the police catch you as they will impound your bike %100 of the time, and the locals in Saigon like to turn infront of you to claim on your insurance, I saw this 3 times all locals doing it to tourists. The little 125s got trashed and the tourists had to deal with the police, and no one will back up your side of the story, so be prepared to pay for bike and hospital bills and bribe money etc.
But like I said i loved the country as a whole.