hello guys

been stuck with a problem
recently have upgraded my system ..now i have 2 ati radeon 4870hd graphic cards
as i was planning tht

will use the first card for the dual monitor setup for the cubase project window my work place with small video for my ref
and will connect the third monitor on the second card for video dedicated for the client for them to see.
which generally is the process in all big studios.

but the now i cant figure out how to do that as when i connect i cant get the video on the third monitor for the client if i get is the small video n when i duplicate the desktop
it copies the same which is not the thing i just need full screen video on the third monitor apart from small video in my project window.
CAN ANY BODY PLZZ HELP ME WHERE M I GOING WRONG or could u please tell me how to get this setup done ...any thing wrong at my end or any other hardware required ?
plzzzz help me with the connections or solutions.

i have win7 with cubase as my main software.

thnx in advance