have a look at this example : http://www.contactcars.com/searchresult.asp?makeid=15&search=true you will see that there is too much options to choose
Are you looking to add custom filters or remove the custom filters that are there. Having custom filters in your search means it most likely will have to be a custom script that knows where the database information is stored. How would you like your search feature to work. Will you give a detailed request?