How to access the information from the network if we donot know the ip address or any other address of the machine which carry that information.

There are freeware products available to scan the network for IP addresses and host names. One is NetScan by Softperfect.

you can actually check the ip of the machine itself
if its windows vista
start >> control panel >> network and internet >> network and sharing center >> manage network connections (left side under tasks) >> right click on your Local Area Connection and left click on status >> click details
it will show you the ip address and other information

Usually if you are using a router, the address of the router is the default gateway . All you need to do to access the router user set up page is to open your browser (Internet Explorer or Mozilla Firefox) and type the value of the default gateway on the address bar and it will let you access the interface and check your settings

if its xp
click start >> run >> type cmd >> on the command prompt (black window) type ipconfig/all >> check under the Ethernet Adapter Local Area Connection area , you'll see the ip and information there

accessing a router's interface are the same steps that I've posted with the vista instructions.. hope this helps.. =)