If you want to do it yourself ... try going from MyBB to either vB3 or phpBB3 ... then to Xenforo.
If your time is remotely valuable ... ask SchmitzIT to help you.
He's helped alot of people.
Jake Bunce is amazing at conversions ... but he'd be more expensive.
As DD stated, there is currently no direct importer available, but an intermediate step can be used to make it work. If you're interested, check the link in my signature for our services, an idea of the cost, and a look at what some of our customers had to say about ut and our services