adding a custom search bar

I need some help being pointed in the right direction. I need to add a search bar to my site.  Not something as simple as search the entire site or search the web though. What I am looking for is being able to search by specific criteria on the site.

I want two input boxes. The first will the search criteria that the visitor will search for. The second will be the specific area to search - a drop down menu with cities (San Fransisco and Brisbane for example)

For example: (first box) carwash  /  (second box drop down menu) San Fransisco

Then the search will yeild all results with anything with a tag of a carwash in San Fransisco.

I hope this makes sense!

Thanks for the help!