Crystal Reports in web application

I am developing a web application in asp/SQL srv 2000 & would like to do reporting in crystal. My users are aroung 20 & at a time maximum 5 will be simulatenously viewing reports. I would like to know which crystal report version should i buy to make it very much cost effective. Can i buy only web server with 5 liscences or i have to buy total developer edition. Currently i am using 30 days evaluation. I have visited crystal decision site & posted this also but not got any answers from them.
Can any one explain me ??