The NETSH command (NETSH.EXE) allows you to change network settings programmatically, for example through a batch file. This may save you from buying commercial programs like NetSwitcher.

The following link explains the NETSH command.

http://www.microsoft.com/resources/documentation/windows/xp/all/proddocs...

Please check also the links on that page, particularly those for Interface IP and WINS.