People in Austin swear you need a title to register it. TxDOT has assured me you don't need a title.
They told me that I needed proof of insurance, a safety sticker, and a bill of sale to register it, as well as a driver's license. Apparently that will get you registered.
Let me dig through their emails so I can post what they said in their own words.
I haven't tried it because I'm moving away from Texas in a few months, so I don't know if they were on crazy pills or not.