have a look at
http://www.google.com/webhp?complete=1&hl=en
from what I can gather they are using AJAX to get client side javascript to
call a web service. (This makes the whole thing more dynamic)
You could write a simple web service which accepts a string uses it to do a
'word%' type sql filtered search and would only return relevant rows as some
kind of delimited string and use javascript to populate the list box
Another option would be to have a popup window which allows you to search
the list , the datagrid returned when clicked would pass the Text and Value
back to the parent window. This would be kind of like those popup calendar
controls
Cheers
Felix