If you want to take a look at our site we do what you are talking about and we do an image for monthly specials and make it clickable. You can see the site at:
https://www.swansoninc.com
The bad news is two things. One your client is just going to have to learn to get their hands a little dirty (depending on what they want to do) and it is not too bad. The image(s) on the main page would be controlled through the admin log in, then go to tools, define pages editor, and then edit define_main_page.php.
If the text editor is set to plain text, you will want to change it to htmlarea. Now you can add custom code to your hearts delight along with tables, images, formatting, etc.
Give it a try and see what you think. Once your customer does it a few times it will become old hat. The only other warning I can give you, and it vary's from host to host, is if you are using secure (SSL) logins the image(s) may not appear on a secure vs. non-secure login. You or your customer will need to learn what that path is and code it in the define_main_page.php accordingly. And once you set it up and replace images from time to time, just be sure to upload them to the same directory and just change the image name and not the path.
Hope all this makes sense, and Good Luck :D
0be1
