You can brand your site in different ways.
One of them is with themes, there are some built-in themes you can use
or you can create your own. You have to know something about css en
to find the classes used on your site you should use iedevbar (or
something with the same features).
this link will show you how to create en custom theme :
www.sharepointblogs.com/.../easy-way-of-editing-cu\
stomized-theme-in-moss-2007.aspx
An other possibility is ajdusting your masterpage, then you can hide
some controls or add some, change the layout completely. With that
you can make your custom core.css for the right colors and images.
You can find a lot on heather's site :
www.heathersolomon.com
In the beginning it's a lot looking for the right classes but once you
get into it...