[html-formfu] dynamically filter a Select list

[Ascii King]

I want to dynamically filter the amount of data returned when populating 
a Select field.  The select field I am using has too much data and 
causes the form to load very slowly.  I have several of these select 
boxes, that pull down different data. I need to be able to filter what 
data gets into the boxes based on choices the user makes.

For example:
The user wants to select a doctor from the drop-down list.
The user knows they want a doctor who'se name starts with 'L', but the 
drop-down box contains every doctor.
I would rather the user just get a select box that conatins doctors that 
start with 'L'.

How can I cut down on the amount of data that is passed to the form on 
load? The only solution I have thought of so far is to give the user a 
text box to enter in the initial of the doctor they want. I assume they 
would have to get this text box before they got to the actual form.

Is there a bettr way?