Without knowing exactly how you are connecting to the Internet, it's almost
an impossible question to answer.
IF you are connecting via a router which then goes to a DSL modem, the
Gateway is the IP address of the router.... from your next posting, the DHCP
Server and the DNS Server are the other side of the DSL modem... your ISP
should have given you the IP addresses of the DNS Server to imput in your
TCP/IP settings and in the configuration setup of the router.
However if the ISP came to your house and installed your DSL connection, you
should contact them to fix this as they usually own the DSL modem and if
you're not familiar with their equipment, it's probably not a good idea for
you to go messing around with their stuff.