Make the larger sections bolder, with lighter face pages below them in the left-side menu. Frames divide the screen into two or more areas, and use separate scroll bars to scroll up and down each area. The advantage of frames is that they keep the menu constantly in view. But frames create more navigation problems than they solve. And pages that happen to be indexed usually come up without the frames structure at all, completely dismantling the navigation system.
Many sites are low in the search engine listings because of frames.
They make it difficult to bookmark any but the main page, so customers who like a particular section of your site won't be able to get to it quickly. The scroll bars look ugly. Some browsers don't print content from frames correctly. Frames make it clumsy for people with 640 x 480 monitors to browse your site. Fixed-width frames often hog too much of the screen, leaving just a small area to read the text.