hi 
, i'm new to an arduino. Just planning to do a project on controlling a remote controlled car using PC(keyboard keys). Can someone help me out in some concerns that i have? First of all should I be using a microprocessor? If yes, why my best option should be an arduino? Which arduino will be best suited for this project? Also some advices on sensors to be used and other electronic concerns
Very broad question. You probably need to do some google searching to see what others have done in the past. Generally you will need a program running on your pc to capture the key strokes and output to some type of gizmo connected to the RC transmitter, assuming you still want to use the transmitter.
Hello deepuuus,
Take a look at a project that i did some time ago:
http://sites.google.com/site/electronicprojectsprogramming/control-an-rc-car-via-pc-using-xbee
You may find it useful.
Welcome to the electronics world! 
And yes, google a lot!