This is something useful for all you programmers out there!
Version control is usually a subject considered when there's a team of programmers involved and keeping track of changes done to the code is vital. But I, as the only programmer on my projects, I find it priceless.
Case study number 1:
-taking phpLinkDirectory and adding new features to it for my own use. This means I sometimes have to modify the core files provided by the authors. But what happens when they release a new version? Do I have to do everything from scratch? No! The Subversion system shows me exactly what files, what lines and in what way I modified for each feature added so applying the changes to the new version is a breeze. Priceless.
Case study number 2:
-Rollback. Adding new features to an existing program you made can be very tempting. Sometimes too tempting. Not once I found myself wanting to rewind everything back to the stable point I was a few hours ago. Ctrl-Z can help, but you're very limited. Subversion does it with just a click.
It's a 100% open source client/server program. The server is available at the subversion project home. You have the option to build it from source or download already made binaries for most platforms from Linux and Solaris to Windows.
As for the client you have more than one option but by far the easiest to use is Tortoise SVN. It integrates directly with your Windows Explorer and you're ready to start in a few minutes using virtually any programming language.
Not in the last place, you should get the SVN book. Free of course ;)