I dont know about streaming the web cam thats what its cauld thats all i know maybe use java for that or jsp (java server pages) for the chat you need a database(mysql, sql, sqlite, derby, and more but those are the best) and serverside (php "connects directly with mysql",asp.jsp,more) have the serverside code read the database then display the results also have the server store the data into the database that the user is going to say and have the page refresh itself if its a instant chat use javascript for this the video your options are adobe flash or flex "flex is flash but its a markup language you have to compile and its free" or use the embeded video player not very secure" or ativex "only avalable for ie"
hope this helped
ps twitter was made using ruby