As for sql server 2000, you can modifty the port as following steps.
1) Open "server network utility"
2) In the "Enable protocols" choose "TCP/IP" and click "properties"
3) You can set the port in the popup windows.
4) Open "client network utility"
5) Choose "Alias" tab and click "Add" button
6) In the window "Add network library configuration", choose the"network libraries" as "TCP/IP"
7) You can input the server alias and the server name and ensure "dynamically determine port" is clicked. That means if the default porthasn't been found, it can choose another port dynmaically.
You can infer the links.
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/architec/8_ar_cs_9okz.asp
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/instsql/in_runsetup_77g3.asp