hii,
currently my pc is installed with windows os , but i want to use linux (ubuntu)os in the same pc along with windows os .
how to proceed please help...

In short defrag you're windows partition
Shrink you're windows partition to make room fore Ubuntu .
Install Ubuntu alongside windows .
In this way you get dual boot .
And there are also lot of thread concerning a dual boot .
Normally it is not difficult to do .
To by on the safe side backup you're drive before installing .

Rephrased a little more clearly:

1) Defragment your Windows partition, using tools inside Windows.

2a) For Vista or newer, use tools inside Windows to shrink the Windows partition to leave unpartitioned space in which to install Linux.

2b) For XP or older, boot the Linux install CD in "liveCD" mode and find the GUI partitioning tool and use it to shrink the Windows partition.

3) Run the Linux installer. Pay attention to the questions that ask how to use the disk. There will be a choice to use the entire disk (destroying Windows). You don't want that. There will be a choice to use just the unpartitioned space. You want that.

The Ubuntu installer will set up dual boot with Windows automatically. Any other questions you might have are already answered in the many other threads here at LQ that discuss "dual boot", Ubuntu, and Windows.

Or install linux in a virtual machine.

Kind regards

An even easier way to try Ubuntu out is to use Wubi. No need to partition your disk at all. see http://wubi-installer.org/