I've been going through the process of getting a title for a former dirt-only bike. In Wyoming, it's not very tough, but I suspect in part that the process is a bit easier for me because of a particularly helpful clerk at the local County Clerk's office.
All I need to do is this: Provide a notarized bill of sale for the bike. Add the necessary lights, mirrors and DOT approved tires. Have the VIN number on the bike inspected by a sheriff's deputy, along with the lights, mirrors and tires. Provide an affidavit that I added the lights, mirrors and tires to the bike to make it street legal. In the end, I get a title and a license plate.
Unfortunately, it's not that easy in other states, and like I suggested, it probably should not be so easy here. In fact, when I first read the statutes on vehicle titles, I concluded that it was not only difficult, but impossible to do this in Wyoming.
That said, I've read about title services in other states where a somewhat shady service thrives, providing titles for cars and motorcycles that lack them in their home states. I don't remember which states have the lax laws that facilitate this process, though. Do a Google search for "replacement car title" and you should find a few of these services.