Hi Shawn: I don't think there is a need to seal your concrete floor prior to adhering carpet. You can put down a 4 mil plastic sheeting moisture barrier, but I don't like this idea much either. If moisture comes up through the concrete, its best to use a latex or moisture permiable adhesive and just let the moisture rise. Trapping it (if it is there at all) under plastic is not a good idea.
Most lineoleum (or vinyl flooring) and its adhesive, that I have used, will act as a moisture barrier by itself.
What I have found does help adhesion is to etch the concrete surface first with a mild acid. This seems to have the effect of making the concrete surface very clean and ready to receive and bond an adhesive.