Excel 2003 Small VBA Coding Project

I have a work sheet I use for quoting. It has 2 combo boxes that are linked, one for category and one for product. What I need is when I enter the Category Combo box if I type the letter L it will automatically go to the Categories that start with L. When I click on a Category that starts with L it automatically makes the products that are associated with that Category in the next Combobox drop down.