All good development companies have rigid source control procedures in place to manage different versions of their applications. Unfortunately most developers fail to bring the same level of discipline back to their personal application development. From a Microsoft developers point of view, this is probably due to the fact that Visual Sourcesafe is complete rubbish and most of the open source solutions require console configuration and are aimed at the linux market.
There is however a very good port of SVN to the Windows platform called VisualSVN Server. When coupled with a cient application such as TortiseSVN, you have a very solid source control solution for the windows platform that can be configured in under 45 minutes. I currently use this setup to manage all the source code for my umbraco and monotouch applications.
There is a comprehensive guide to configuring VisualSVN Server here.