I really have no experience with crossbows or what you should look for. I think one of the more important features is some type of aid to pull the string back. I've heard that consistenty in this leads to accuracy. There is a crossbow forum under the archery boards that would probably help you out more. Good luck on sticking something
edited: heres the link
http://www.huntingnet.com/forum/tt.aspx?forumid=96