Salvage title

Go to your DMV or wherever you get your plates/regristration and talk to them. Here in michigan we need to get an inspection from the state police saying that the car is road worthy. It actually isn't that hard of a process from what i saw but i didn't go all the way through it.

Depends on the state, here in SC, I went a slightly different route, and got a Magistrates title for my $50 body shell.

The salvage route sounds easier.

If you owned the car, and had tags and title, why not just continue it.

If his insurance paid him for it and he bought it back, then it has been marked as a salvage vehicle and the DMV will not renew tags on it. You have to just see what your state's process is, but basically they do have to examine it and deem it roadworthy. But be warned, your insurance value a lot of the time is basically zero from now on, even if you fix it all up. You will probably only be able to get liability coverage if the insurance paid a total claim on the car once before. It would pay to check on that before putting a lot into it.
Good luck!