I can't help you with ASP-specifics since I haven't done any, but I can tell you some general tips to point you the (hopefully) right way :
The nice and elegant way
Your output will be plain HTML -- hence, ASP can't help you directly since it's not running at the time.
What you need to do is write a simple Javascript function that connects to another page, and fetches the page output ( AJAX-style ). You can then just call the page with a few GET parameters like
http://mydomain.com/assests.asp?choice=1
That will call the assests.asp page, and give the parameter choice=1. That page can then connect to the database, do whatever processing is needed, and return the options for the next combobox to your Javascript.
Javascript then gets that output and dynamically fills the second combo box.
That's the nice, elegant, expandable way of doing things.
Edit: Just found a person who's done a small example of this
here . It's in PHP but the PHP part is just an echo, the rest is Javascript
The quick and dirty
If your first combo box has only a couple of options though, and is only a quick work, you can just add as many hidden divs as possible options, and only show the one needed. Quick and dirty.
E.g. if your first combobox has 5 options, make 5 DIVs that are hidden. When the user picks one option from that combobox, unhide the appropriate DIV, and rehide the rest ( in case he changes options ).