DSN Names for local intranet sites

Hi,

How would you go about setting this up in a windows 2000/2003 server
environment that is running ISA Server as the internet firewall/proxy (this
is external to the intranet, ISA doesn't interact with the intanet) and this
is all on a domain cluster... what I have is three intranet sites at

//server1 port 21
//server1 port 85
//server2 port 21

what I want to do is map them to a host name so server1 at port 85 loads at
http://intranet/ and server2 port21 loads at http://extranet// and server1
port 21 loads at http://bugtracker/ is there anyway to do this easly?
thanks!