The LabWindows/CVI instrument driver is just set up to send the correct GPIB commands and read back the responses for your particular instrument. Typically, in an instrument model line, the commands to Initialize, Configure, Start Waveform, etc. will be similar if not identical.
So there is two things I would suggest trying.
1. Ask the instrument vendor to see if the ds340 and the ds345 accept the same GPIB commands.
2. Download the driver from here:
http://www.ni.com/devzone/idnet/
and test it using your instrument.
Winston L
Applications Engineer
National Instruments