what size tire do i need?

hey i want these rims but i dont know what size tire i need to fit them, i dont understand the sizing on tires, if sumone could explain that would be awsome, and where can i find cheap tires?

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&item=7906923771&category=43958

-Tyler