http://www.microsoft.com/windows/directx/default.mspx Is the link for DX9.
But i agree with Nigel, sounds like graphics card driver conflicts to me or the cam its self. Dropped frames usually means that your missing frames out of a sequence. IE: a 28fps (frames per second) bit of footage might only have 16 frames due to drops.
Sorry i cant be more specfic this time barry! :-(