Hello,
It looks like Agilent/HP makes the 8990A, but I was not able to find a driver for it that we or Agilent has written for this device.
Since I am not familiar with the 8990A, I cannot recommend which drivers might be similar, but you are pointed in the right direction. Agilent themselves might know more about which models use similar command sets so that you can modify a driver easily.
Hope this helps.
Scott B.
Applications Engineer
National Instruments