As in Windows we have Video memory and we can access it through C programs, do we have anything similar to that in Unix and similar operating systems. If we have some sort of Video memory in Unix flavours, then how can we access it through C programs.

Video memory is a PC thing. Unix runs on a LOT of different hardware platforms, and was around before PC's. I/O operations are initiated in kernel mode.

The ncurses library supports some screen operations, which allow you to get data from what is on the display. Check that out.

Yeah, and even with Windows, you usually don't access the video memory directly. AFAIK, most apps will use the GDI lib or DirectX/OpenGL for bitmap graphics. And in fact, most apps won't need bitmaps at all; they will just use GUI widgets.

If you need bitmap graphics under UNIX, take a look at X11 (Ximage functions or the MIT-SHM extension are prolly what you should use), GGI, SDL or something with OpenGL.

Can u please tell me where can i find good help about the Ncurses library. I have tried to find some material about Ncurses but was some unable to find some useful information.

http://dickey.his.com/ncurses/ncurses.faq.html
http://en.tldp.org/HOWTO/NCURSES-Programming-HOWTO/
http://web.cs.mun.ca/~rod/ncurses/ncurses.html

A google search for ncurses gives 580,997 results just like those three.

Cheers
ZB