some themes have a page listing with drop down menus. If this is the case you can create a page called "Clients", then create your additional pages with their info, and set the "clients" page as the parent page.
Then when you look at your blog, you should have a page link that says "Clients" and when you mouse over it, the other menu items will drop down.
This is recommended if you are not into HTML.
You can also see an example at my website,
Damon Pena's Photography at the top of the page under Galleries