Windows 95, 98, ME, NT
access the network control panel
under TCP/IP properties, check the "obtain address automatically" box
Windows 2000, XP
Goto the "Control Panel"
Click on "Network Connections"
Right click on the appropriate connection, usually called "Local Area Connection", and select properties
Click on "Internet Protcol (TCP/IP)" and select properties
Check the "obtain address automatically" box
check the "Obtain DNS server address automatically" box