.I am new to using arduino and this was just like my 3rd project. I was running a line following robot circuit on my arduino duemilanove, and suddenly the board stopped responding. I took off all wires and checked the board for heating. The area right below the Atmega328 was super hot. what does this do to affect the board and what may have caused this and how could I repair this, if this can be repired at all.
Sounds like you overstressed your outputs with too much current going thru the pins & damaged the ATMega chip. Likely need to replace the chip, and put some current limiting resisters in your outputs, or possibly add external drive transistors that can handle more current for whatever you have connected.
Post your schematic so we can give better suggestions.
Update your profile to include location so we can suggest country specific help for locating parts if needed.
Robert
HI ROOPAK ,
well your name sounds indian ! actually even i am roopak 
you'll need to get a atmega 328 and replace it but as crossroads said you need to fill out your profile so that we could give more details there are many places you could get a atmega mcu 