Hi,
Desktop Communicator can be found on the ftp.usa.hp.com FTP site. The login is connect and the password is 2GetConn
The software can be found in the folder /PC_Applications/Desktop_Communicator/DC_2_7_1
As for tricks to get it working with a VCX Connect 200 running 9.8.15, generally following the Desktop Communicator User Manual works well.
A key point is ensuring that the Phone Profile is configured to enable Desktop Communicator (either regular or Outlook Edition) as the Softphone.