Regarding Linux the preferred driver is the USBTMC driver from the Linux kernel as of version 2.6.28.

In case an older kernel is used, NI-VISA can also be used or the open source driver which lead to the current kernel driver can also be use. This open source driver can be downloaded from this location http://www.home.agilent.com/upload/cmc_upload/All/usbtmc.html. An example of how to use this driver can be found in our Linux HOWTO.
Also a libusb can provide a solution for older kernels.

For examples please check the above mentioned HOWTO for now. Using the recent kernel driver will be covered in this section soon.