You can easily dig around for more sources, but I've attached the wiki link, which has some information about fuel usage and many other uses. From what I can remember it's about as viable as biofuels from corn (maybe a bit better) but still not really production quality. Hemp's biggest advantage is the strength of it's fibers.
Anything that can be made from a hydrocarbon can be made from a carbohydrate. If hemp got the same subsidies, protections and considerations from the government that petroleum does, I suspect it would be cheaper than petroleum in the long run.
Could you clarify this statement? Are you saying hemp can be efficiently used as a fuel?