If you are dealing with a HUGE (infinite) number of results from a query, may I suggest the following:
Instead of dropping down an infinite (select * from table) number of results, do a small search on the db to limit the results. I.e. I am looking for client <input type = text name =search>
Now, do a search on the db with a LIKE statement to norrow the number of members of the drop down.
With the result set of the search, build the menu with
select * from table where field LIKE '$search'
or LIKE '%search%' if you'd like.
while/list through the result with echo "<option>$var";