HOw to add search by keyword for every listing types?

Hi,

How do I add a content box with search by keyword (for specific listing type) function for all categories?
For example, listing type: computer has sub-cat: laptop and tablet. How do I add a search by keyword (for listing type computer only) to both categories laptop and tablet.

Thank you for your time

I'm still looking for a solution for this matter. If anyone has any idea, I would be much appreciate it.
Thank you

we have been trying to figure this out for days now and not getting anywhere. i have a classified site with "Motor", "Property", "Jobs" and "Everthing else" as listing types. The problem is the top search bar will only search in listing type " listings" (now renamed everything else) and ignores all other listing types. The drop down menu from any category arrow only lists listings from listing type and none of the other listing types. its so annoying. why allow the admin to create different listing types if they cant be accessed from the search on the home page unless you create another keyword search bar, which is limited.
If you get an answer to this issue can you share it and we will do likewise.
THanks
Niall