Dynamic sub menu categories

Hi folks,

Hopefully someone can help out a "lesser mortal" with basic skills here!

I am developing an 'add record' form to update a database (PHP/MYSQL) and would like to be able to set the items in a dropdown sub menu based on a choice from the previous menu.
e.g. first category is chosen from a drop down containing 'Sparkling Wines, White Wines, Red Wines' etc
second category contains sub categories for the above, e.g. 'Champagne, Sparkling Reds, Chardonnay, Riesling, Merlot, Shiraz' etc.
Is there a way to populate the dropdown for the second category so that it only shows the related options (e.g. Merlot and Shiraz if Red Wines is selected) rather than the entire list?

Any help or suggestions would be greatly appreciated!

Thanks in advance,
Graham