mambo is a cms and within the admin area you are able to add components and modules in seconds - OSC is great for what it does but unfortunatly it is fairly difficult to change the look if you are not used to it - very stock

Mambo has a component called PHP-Shop that you can install in seconds - also there are thousands of templates out there purpose built for it so you just upload and install through admin and choose the template you want to use

I can show you an example of a site i am working on with it installed (Mine) if you want to PM me I will give you the url)

Regards

Mark