Hi Ailish,
The express VI will most likely not be providing you with channel options for acceleration readings because the values read by the USB 6009 will just be standard analogue inputs. I would recommend that you take a look at the following article and simply swap out the myDAQ being used here with your USB 6009. The coding should be essentially the same. You will notice that the conversion from voltage to acceleration is being performed in software.
-Measure Acceleration using a 3-Axis Accelerometer, myDAQ, and LabVIEW
http://zone.ni.com/devzone/cda/epd/p/id/6407
I hope that this helps.
Kind regards,
Daniel T
Account Manager
National Instruments UK & Ireland