I think every group has their own spiel for getting new people into their group, but some are effective and some are not. Here are some effective articles that deal with explaining the hobby to the layman and new recruit. This would be great material for units looking to actively recruit in formulating materials and Web site blurbs.
The first is an article in the Emmitsburg Area Historical Society newsletter. It has a great explaination of the hobby, albeit from the perspective of the F&I War. Sutler.net has a very high-level explaination of Civil War reenacting, which is well written. The 1st Nebraska has a more in depth Q and A article that covers costs and such. The Wikipedia has a nice write-up on reenacting in general, and although it is mostly a good write-up, the Civil War reenacting wiki is a little slanted against authentic reenactors. The best newbie information page is on the Our Hearts Were Touched With Fire site that I also covered a while back.
If you're looking at the civilain side then Fanny and Vera's site is a great place to see what you need. A great introduction to the hobby. I've covered this site before, but it's nice to reinterate a useful site every so often.
On Amazon.com, there's a book just on this subject, So You Want To Be A Civil War Soldier. I haven't read it, but it looks like a decent intro to the hobby.