Auto lookup in dropdown

[poppy]

I have a dropdown on a webform which lists employee names.

When the user sets focus on this combo and enters a letter
such as "M" then the displayed values jump to the entries
which start with M. If the users then hit "A" the list
jumps to the entries starting with A.

This is usually fine but my users want the list to act
more like an access combobox. When the User enters
the "A" as the second key they want the list to jump to
all entries starting with "MA" and not "A".

I have no idea how to achieve this as it must be done
client side as I cant do a round trip with every key
depression.

Can anyone tell me if this is possible and maybe give me a
few pointers ?

Thanks in Advance