It can be difficult when one partner brings up the subject of swinging for the first time, particularly when only one of the pair has any experience with it.
First off, you need to get her to agree that she won't actually do anything until you are comfortable with it, if that ever happens. Next, you should educate yourself as much as possible about swinging and swingers. I can't think of a better place than this board and we will try to help you as much as possible.
Getting Started is one link you should visit, as well as checking out other threads in the
New Swingers forum.
Then, talk at length with your wife about what she wants, why she wants it, how you will be involved, how you feel about it, etc. Ask her to tell you how it will improve your relationship, or at least not hurt it, for example. Find out, if you don't know, how she and her ex started swinging, why they did and whether it contributed to their breakup.
Come back and ask your questions here. There are a lot of people who will share their advice and experiences with you.
-B