Use Sub Drop-downs Or Sub Forms

I don't know what to call what I want, but here is the description. Can I use sub-Lists?
I have a dropdown that conatains a list of products. When a user chooses an item, I want another drop down or anything that will allow them to then choose the specific category.

For example:

#1: I have cars and trucks.

When I user selects cars, I want a dropdown to give them available cars to choose from.
Say for instance the user selects Ford. Then I want them to have the option to choose
from the list of Fords. Escort, T-bird etc. Their final choice is what's sent to the DB.
#2: Also, I don't want to give them the option to enter a date into the DB. I have a field in my DB design "timestamp". I want this field to be automatically populated server side once the data is submitted.