Print postal barcode on envelopes

I am printing an envelope and want to convert zip code to postal barcodes. What do I have to do? I am using MS Office Word 2010. 

You do have two ways to generate barcodes in Word. One is barcode font, the other is barcode control. Both need installing in your Word first.

 I am also planning to draw some linear barcode in word. But not postal barcode, will the control or font you guys referred to will be OK to create other barcode? 

MS Word 2003 and eariler version provides the postal barcodes. However, it is not compatible with the Intelligent Mail barcode specifications and has been abondoned in Word 2007. So a third party barcode generator is preferable.