configure our mail server

I have an ubuntu mail server on karmic 9.10 running Dovecot IMAP/POP3 Server, Fetchmail Mail Retrieval, Postfix Mail Server and Sendmail Mail Server. I am trying to get this up and running with roundcube or openwebmail and I am having issues. I need one user to forward all mail to a gmail account for now and give me a break down of what was done. This needs to be done asap for under 100 bucks gaf. thanks guys!