Resin kits are limited run kits, usually put out by the "cottage Industry" as it were. Rather than being made of injection molded sytrene plastic, the tooling of which is prohibitively expensive except on a large scale, these kits are made from two part resin molded in a rubber mold. (You can get your own resin molding supplies from a number of vendors, to make and duplicate your own parts). As such, there might well be an esoteric kit that is not available as an injected molded kit that is available in resin, although being limited run, these kits are usually quite expensive.
For the most part, you can use the same sorts of paints and techniques on resin that you do on injection molded plastic. The major caveat with resin, is that the parts will be covered with a mold release agent, and must be washed prior to use. Soap and water is usually fine for this. Failure to do so will result in poor adhesion. I heard from a ship builder from another forum who forgot this step, only to gave a complex splinter camoflage scheme pull off with the masking tape. Resins are kind of oily as well, so most builders do use primer with it.
For drybrush and wash techniques, check my post near the bottom of this thread.
http://www.finescale.com/fsm/community/forum/topic.asp?TOPIC_ID=41283