Well that's the general idea behind the CMS I'm building, they won't have to know anything. I'm even building in a lot of error checking to make sure they don't do things they shouldn't. The basic idea is not only will they be able to alter content but build new pages too.
Here's a screenshot from early developement of the first stage where a page is actually created:
After error checking:
All pages will be gfenerated from a single file completely database driven and rewritten using htacces to make it appear to be real files. I won't be using URL GET parameters to retrieve anything. Basically the client is going to be able to go into this first panel above and "create" the page which will make it active. The second step will be picking an appropriate template for whatever content they want, add the content. Lastly you'll go into a URL panel to add it to the navigation.
Still a while before I'll be done with it but so far so good.