Hey Arjun, 20K is cutting it a li'l too fine for a gaming cpu!
Anyways, will try to stick withing your budget.
Mobo - Gigabyte GA-880GM-UD2H for Rs. 5775http://www.lynx-india.com/index.php?productID=13441
CPU - AMD Phenom II X2 550 for Rs. 4436http://www.lynx-india.com/index.php?productID=11346
PSU = Coolermaster extreme power plus 500W for Rs.2839http://www.lynx-india.com/index.php?productID=706
RAM - Kingston DDR3 4GB for Rs. 6300http://www.lynx-india.com/index.php?productID=13478
HDD - Seagate Barracuda 7200.12 @ 1TB SATA Internal Hard Drive for Rs.3486http://www.lynx-india.com/index.php?productID=8657
I'm quite certain that the prices you get from the market will be much cheaper than the ones on the net! Are you in Delhi? If yes, try going to Nehru Place...you'll get great deals there!
Buddy, we're yet to get you a GPU!
The above itself went a tad over 22K. Will you be able to put in a bit more? Say, about 8K or so?
I'd suggest you open a fresh thread in the home built systems forum if you're considering getting a complete new rig.