Yeah I have had a little peruse, will be heading to the Peace Cafe for definite. I'd consider renting a motorbike myself, but my Mrs is a terrible passenger seat driver, god knows what she'll do when I'm on two wheels.
Think this is the guys: http://www.dalat-easyrider.com.vn (and oddly here too: http://www.easyrider-tours.com)
Apparently there are young inexperienced guys who'll jump on travellers the moment they set foot of the bus, so avoid them. We headed to the Peace Cafe and chatted with our potential guys first - we felt really comfortable with them and they didn't pressure or hassle us to book so we felt reassured they were the real deal. Their names were Mr Thau and Mr Thai so perhaps you can track them down!