Steve,
You'll definately want to try out regulators before you go out and buy. My first reg was really bad, my throat would be burning after about 25 minutes or so, and I even found myself taking in salt water just to try and get something wet in there. I'd drink about a 1/2 liter of water after each dive just trying to get my throat back to normal.
Now my problem was solved with a different regulator. It wasn't until I was almost home when I reached for my water bottle and realized I hadn't sucked off of it all afternoon. Some regs are better than others with dampening the air that is coming out of the bottle. I have an Apexs. I hear Posidon is really good, as well as Scubapro, and I'm sure others will speak up on other regs that are good.
Alternatively you can solve it with other means as well. Some people talk about bringing a water bladder down so they can stick the hose in their mouth and get a drink of water. Definately an excellent idea to both deal with dry-mouth as well as keep your body hydrated. There are also filters you can put on the line to moisten the air as well.
The number one thing if you have issues with dry mouth is to shop around for regs and be sure to try a bunch before you buy, and hopefully you can find one right from the start that works well for you.
G'Luck!