versioning ur program

From: A`WaRe (awary_at_msn.com)
Date: 04/29/04 

Date: Thu, 29 Apr 2004 04:49:30 -0700

hello
hope this is the right place to my question...
i wand to know how to give version numbers to my program like z.x.y
when i change the z and when x and when y ??
also what is diffrient between alpha/beta versions?
it'd be appriciated if there's good documents on this..
THA..