Hi stevet170,
Welcome to the Q&A Board!
Yes, you will need an adapter if you want to use an UV lens. It's a wise idea, since it helps protects the lens! Please note, however, that the lens cap of the S2 will not fit on the filter, so you will have to purchase another one for use with the adapter and filter.
As you know, Canon sells these accessories for the S2 and they can be ordered from places like Amazon and photo websites. A local camera store may sell them too.
Many people rave about the accessories from LensMate. They sell 52mm and 58mm lens adapters. There is a FAQ about when and why you may prefer one over the other. Even though I prefer the look and fit of the 52mm adapter, I'm getting the 58mm one since I already have UV and Polarizer filters with 58mm threads.
http://www.lensmateonline.com/S2.htmlOn the order page, they also sell other accessories including filters.
http://www.lensmateonline.com/buy6.htmlYou can call and ask questions, and place orders by phone. There phone number is not easy to locate at the site, so here it is:
206-772-3048
Related reading: Digital Camera Accessorieshttp://www.digicamhelp.com/digital-camera-accessories/index.htm