I am a newbie in aero-models but have mede a few boat models (balsa wood and Aluminium sheet) but without RC. Now I wish to continue this hobby and purchase a radio control(2.4GHz) also I am trying to build one too, I got some good 2.4GHz transceivers for that (1.8Km range). Can somebody tell me how to obtain permission from the authorities to own and use a radio control.My location is MOHALI (PUNJAB) and the local authorities are not aware of rc modelling. Please also send a copy of one such permission letter for the reference. My email-
  thankx in advance.

I am not sure there is such a thing ! 

Looks like it is only common sense measures for now, like :

1.  Do not fly near populated areas.
2.  Do not fly near restricted areas (airports etc).
3.  Even in open fields away from people, have someone to prevent kids from getting curious and running into the field etc.
4.  Seek permission from the owner of the land beforehand, if you are flying in private land.

The closest you can do in terms of official paperwork right now seems to be buying a WPC approved radio from IndianHobbies.com (I am not aware of others which are WPC approved), and ask them before purchasing to give you a copy of the WPC approval for that radio.  This would provide you at least with some piece of paper (how much that would help you in real life is something to be seen yet!).

Any comments from others ?

Yes Anwar, Don't try to make your own  Radio even if you have 2.4Ghz RF module. Lots of RnD goes in Tx/Rx module in area which is usually trivialized by most Electronics DIY  - Error correction. As Anwar suggested, buy a standard OEM Tx/Rx combo from range of Rc LHS in India like Indianhobbies.com, RcDhamaka.com, rotor.co.in etc. If you are too model/cost conscious and have some one coming from US who can carry the Radio, world of choice is open to you.

For boats, I think you would need Rc Car kind of 2Ch Tx and special Marine Rx... check out in appropriate forum which are the best brands suiting your pocket.