create a select list from another select

[Anon]

Hi
Excuse me... My title was not so descriptive, because of the limitation of characters...

Here comes my problem:
Im trying to create a select list in which the options will be added depending of what i have selected in another select list in the same page (Im doing a query from the results of another query, depending of what the users wants to select)

Im having headaches because of that...Can anybody help?
Thanks