Need to host 2 external sites with 1 IP

At this point it is down right confusing... I'm helping a friend try and get his work server to temporarily host a 2nd web site for a client of theirs. Problem is that the hosting location is a MS 2003 DC and they only have 1 external IP address. To make matters worse, they only have a little Linksys router (for this particular office) that will only forward port 80 traffic to one address.

Any suggestions???