Owner Adding Content to a site

[vancity]

I am helping a friend build a basic web site, I can handle html, etc. What he needs to do is be able to add the same type of info, with pictures on his own about 20 times a week, (preferably without calling me 20 times a week to do it) - He is selling cars, so I need to be able to enable him to add new cars to his online database and upload pictures of the cars (which he will then need the small picture expand in a new window)
I am sure this is easy for those in the know, thank you in advance for any insights

[Wickham]

A Content Management System (CMS) is used so that an untrained person is only allowed to make edits in certain places.

Two CMSs are frequently mentioned on this board:-
Joomla has a lot of capablities http://www.joomla.org/

Snippetedit http://www.snippetedit.com/ is for simple edits of text or images. There is a demo. If you allow someone to upload images, they may upload images too big or small and wreck your layout unless you put in sizes in the code like
<img style="width: 300px; height: 100px;" src="image.jpg" alt-"Image decscription">
and only allow the image filename to be edited which should resize any uploaded images. Also cancel the image sizes in the Snippetedit upload menu.