Result dependent exposed filter list (Views2)

Hello,

I list my content with Views2 set in the taxonomy menu.
I further filter this list with exposed filter placed in a block.

In the taxonomy menu there are main categories (like vehicle).
This list is filtered by subcategories (e.g.: car, motorbike) and/or towns with exposed filter.

I want to achieve to list only the subcategories and towns in the exposed filter which has a corresponding
content in the main list.

Can I do it with Views2 or is there another module?
Or some coding?

Thanks a lot in advance!
Czollli