help me to choose my pc software & other requirements for it

[iS THAT ME]

Linux/Ubuntu is opensource, free.
If you purchased it, claim a refund.

When you order ubuntu online, they charge for media and shipping. :c

lemme tell you, i got 3 CD's of ubuntu at home, which i got free, from net only. There is a foundation that takes responsibility for developing ubuntu, and thy distribute ubuntu CD's free, for educational purposes.
What you are talking is an ubuntu distro. it doesnt contain only ubuntu, but its definitely bundles with something else.

.......
But, I was using Win 7 on P4, 256MB RAM and no graphics card

You mean you are using on-board graphics card..... No add-on card for graphics... :c

no, I meant NO onboard graphics also...
It was Win7 Developer version first, then RTM, then Home Basic, then i got my PC upgraded...