I would be weary of soldering of I was you. At least with my setup, the barbs and the radiator had, in no way, a tight fit. Soldering is supposed to be used when you have a relatively snug fit. I had the choice of threaded barbs that were too big to squeeze into the radiator tubes and barbs on both ends, which I wound up using.
I tried using solder, but there was just way too much space to fill in with the solder. It still left huge gaps even after I used up a ton of solder and flux.
Plus, I am unsure of how well solder bonds to brass.
What I did was go down to Ace hardware and look for an epoxy that says it bonds to both brass and copper. What I found was this double tube syringe thing that had black stuff in one tube and off-white stuff in another. I think it was called steel weld epoxy.
Anyways, I sanded down the barb I would be inserting and used a wire brush on the inside of the copper tubes in the radiator. The epoxy was a bit thin, so I used masking tape to help keep everything in place. I got everything somewhat set, made sure no epoxy was going to drip anywhere that would impede flow, and let it set for a day. Then I applied another coat of epoxy just to make everything look nice and smooth.
Haven't had a leak yet.
EDIT: be careful with soldering. Remember, those tubes sticking out of the radiator were most likely soldered into place and they will get royally messed up if the heat from a torch reaches the joints. When I did my soldering attempt, I had someone using a wad of Q-tips to keep the joints wet (and cool) at all times.