Quick question

Ok, here's the situation....

I've designed a site for my wedding (Only Graphical at the moment in Photoshop), im fine with slicing and then coding that into Dreamweaver.

Once i've finished designing the site, entered all my content etc, I want my wife to be to be able to update the text on the site and maybe change/insert some images. She has no experience or knowledge of how to do this. I don't really have the time to show/teach her at present. I've heard of Content Management Systems that can be used, but have no experience of this myself, are they easy to set up? easy to use? and which one to use? Open Source Preferably....