The YMM contribution store data in cookies so if the customer selected BMW MX3 it will be already selected for him next visit time.
The make/model/year dropdows in the "Select Vehicle" box are dependent. They show only the makes/models/years that you store have products for.
After the make/model/year were selected the "Categories" box will be filtered. Only the categories that have products for the selected year/make/model will be shown.
Download the contribution and view the screenshots to better understand what it is.
There is a sence in creating an "all products" page and show it filtered just after the customer selected year/make/model . But I don't think that everyone will like it.
So I have left the instructions in the README.html how to make any custom page filtered by year/make/model.
This package contains autoinstaller script. It automatically install the contribution: copy files, edit files, alter database tables.
It saves a backup before any action and make possible to uninstall the contribution.
You will need to do manually only what the script cannot.
It was tested on hostgator.com host (PHP:5.2.4 MySQL 5.0.67) and osCommerce Online Merchant v2.2 RC2a