Custom OSCommerce Drop Down Menu

I have built a farely simple OSCommerce database and need a custom drop down menu to access the database. There are 4 categories, they each need to have their own menu. Each category is structured into makes, then models, then products. The menu will need to behave like this one: [login to view URL] (under performance products). It has you select a make, then it populates a list of models, then it accesses the database for products according to what make and model you have selected. I don't want to edit the source files of the OSCommerce structure, I would rather this be an outside script, if possible, to access the database.