You can get a 3 month multiple entry tourist visa pretty easily. It cost's about $140 for the various fees. You have to google visa agencies and fill the form online. Sometimes you can get 6 month visas also though I can't seem them on line at the moment. When it runs out you can fly to Singapore or similar and apply for another. The Vietnamese don't seem to worry too much what you do once you are there. I'm probably off there soon to hang out in Saigon which is quite fun but more expensive.