It is very dangerous to follow this line of thinking. If you have a lot of information categories, or you are planning on adding more categories as your portal evolves, a horizontal strip of tabs is not going to provide the flexibility you need. Nothing could be less user-friendly than attempting to cram an infinite number of tabs across the top of a page, especially since the standard monitor resolution that most people need to target is 800 x 600. One of the main goals of navigation is to give users a constant birds-eye view on where they can go and what content is available to them. Having part of your navigation scheme constantly off-screen, forcing users to scroll horizontally to see what they are missing, undermines this goal.
Navigation needs to fit the content.
If you have a lot of information categories, a vertical navigation scheme appearing down the left-hand side of the page may be your best bet. Better still, keep all of your links plain hyper-text. If you're worried that your users won't be able to tell where they are without the pressed-in look of a selected tab, have no fear. Provide a simple search with an advanced search option If users are uncertain about where to click to begin their portal experience, they will most likely resort to searching for content. A portal is not the proper vehicle for trying something new.