Select and GO between FRAMES ?

Ok, I now that this is basic, mas I cannot find a way to address a frame starting from another frame. :(

- a classical two-frame website;
- one frame is a left vertical menu;
- the other frame is a "main" where data (small pages) is to be shown
- need to use a few <SELECT> statements, each having several <OPTION> statements on the vertical-menu frame
- when an <OPTION> is chosen, the indicated page should be shown on the "main" frame (target="main")

There is NO need for a GO button, but I would use one, shoud it be necessary.

Does anyone have the right HTML code for this ?

Thanks for any help !