3-state MouseOver with Frames

My problem:

- A navigation frame with buttons which should stay 'on' after clicking it.

- in the content frame there are crosslinks to other chapters, so the button status should also reflect the change.

- have tried with an 'onload' script on every content page, it works, but is awfully slow.

- my current solution you can visit at: http://www.economa.at/test/
there is a 'onmousedown' script on every crosslink, it's ok, BUT:
by hitting Browser's back button the button status of course remains the same ((

Any ideas or prefab scripts for that ?

thx,
Gerhard