I am a C Programmer. Now want switch to Network Programming. Anybody tell me where I will get free tutorials and study materials?

What exactly do you mean by 'network programming' ?

Programming for networks? or Microsoft .Net ?

If it's networks, that depends on the application, but for basic network back and forth, you might check out http://www.gamedev.net, and maybe http://www.codeguru.com, or just google it.

If it's (dot)Net stuff, there are a gizillion tutorials out there, including a lot that come with Visual Studio. If it's (dot)Net you are looking for, you need to give a language before I can get more detailed, but again, one can google on ".Net Programming Tutorial" and come up with many decent hits.