There are posts on these forums for allowing DA to listen on other ports. I'm not sure if there are any to allow it to listen on port 80, though.
The easiest way I can think of to do this would be with an iptables rule (presuming Linux, and not BSD), forwarding between the world on .6 port 80 and localhost on .5, port 2222.
DA is licensed for the IP# for which you bought the license; to change the actual IP# that DA listens on requires a license change available by contact the DA sales department.
You can set DA to listen on any port, but you'd be responsible for changing Apache's main httpd.conf file so apache doesn't listen on the IP# you're using for DA on port 80, since both DA and apache can't listen on the same port, and since by default apache is configured to listen on all active ports.
Paragraph 2 above ... that would be the way I'd try it first.
Jeff