Magento category dropdown navigation

FOA Magento developers I have a client who would like their users to navigate through their categories using drop down menus. eg there will be 3 onscreen dropdown boxes, they will select from the toplevel categories in the 1st box which will load the corresponding 2nd level categories into the 2nd box. The user will then select the 2nd level category which will load the 3rd level menus into the last box. Selecting the last box will take the user to the category they select. like this [login to view URL] The aim is for the users to be able to select Make, model, sub-model where make, model and submodels are normal magneto categories. The box will be shown in the right column. thanks