Multi-Level Dependant Search

I want my advanced search work as:

I have 3 search field: (all lookup table searches)

1. News Main Category
   
2. News Sub-Category (Dependant on Main Category)
   
3. News Name (Dependant on Sub-category, if no sub category available lookup table is dependent on Main category)
   Not all news has Sub category, but all news has Main Category and Name. Using lookup table user selects 1. News Category, according to that category News Sub-Category Shows up and According to that sub category News Names lists but if Sub-category isn't available than News Name is only Dependant on News Main Category (but in look up table News Name is only dependent on News Sub-Category).
   Anyone? please help on that?
   -Thanks
   
   Rumman