Printing different addresses letters/labels

I need to send out mailshots to lots of different people in order to help drum up more business through this recession.

Is there a programme or application that I can use that resembles something along the lines of:

I type out all the addresses that I want to send my mailshots to and press a button afterwhich, all the addresses will be printed on to:

a, Sticky labels which I can stick on to envelopes

b, The letter itself and buy some windowed envelopes which shows the address once sealed..

Any help will be greatly appreciated... Cheers