DHTML menu/frames problem

I am designing a website that has a frame for the top part, a left side navbar and the middle has the information on the different pages
---------------
TOP         &nb sp;   |
---------------
s |           ; |
i | middle   |
d |           ; |
e |           ; |
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I have a DHTML menu nav bar on the side, but because some of the menu is nested, half of those buttons are not displayed because they overlap the middle frame

Any ideas on how to overcome this while keeping my current structure??