The default TCP/IP configuration with most DSL routers uses DHCP to assign the IP Address, Subnet Mask, and DNS servers. This configuration is for users who will not be running network services, such as a web or mail server. This configuration is the simplest and is desirable for users whose primary function will be web browsing, checking email, etc.
From the Windows "Start" menu, select "Control Panel", then "Network".
You will then right click on your Local Area Connection icon and choose Properties.
You will then highlight "Internet Protocol (TCP/IP) by clicking on it and choosing "Properties" below it.
Select "Obtain an IP address automatically" and "Obtain DNS server address automatically". This will automatically enable DHCP support in Windows XP/Vista. Click OK when finished. Windows may prompt you to reboot, if it does select OK.