The title needs to be signed over to you (by the original title holder... your Dad) then you have to register it (assuming that it's required there) When this happens they will take the title from you and re-issue one titled in your name. When this happens they'll probably want (ok not probably... . definitly) want their tax money. If so, then just tell your Dad to write in a few dollars as the sale amount and you should be ok.
That's the official way. You could probably get away with other ways for a while, but when it boils down you're going to have to title it in your name eventually if you really want to own it.
I know here anything with tandem axles has to be registered to pull down the road, single axles do not. I'm sure that won't last long though...