Think of Mambo like DreamWeaver or FrontPage: it's a tool used to generate sites. Sites powered by Mambo don't all have to look the same. Mambo (and many other CMS tools) allows the user to customize the site to look any way they want it.

When looking for a site design team, you'll want to see if they have experience using whatever CMS you want to use. Then (trust me on this, too) have them write you up a series of easy instructions on how to add and edit content. Mambo's very powerful, but the interface isn't easily understood unless you've used CMS tools and understand how they can be organized.

I do have most of that information in an article...I just can't put it online for another month yet. Contracts, contracts, contracts...