This is what I am trying to do:

1. I have a list called company.

2. I have another list called contact and a column using company name
from Company list.

3. I would like to create a thrid list called event. In this list, I
want to use company drop down from Company list and a drop down with
contact name from contact list.

When user select a company name, the contact drop down will show only
matched names based on the selection.

I am using MOSS 2007 and I think I read something before to customize
this. If you can direct me to some web sites or articles, I will look
into myself.