SANE related tools
You can find and download sniffusb here.
You have just to run the SniffUSB.exe program contained in the zip file to start logging usb traffic. Usage detail are available here.
win98/winme patch to usbsniff
usbsniff makes an heavy usage of non pageable memory, the following driver is slightly modified to be less memory hungry. This version is compiled for win98/winme only:
Win 98/Me usb filter
An improved sniffusb
You can get at UsbSnoop PCAUSA a newer and improved sniffusb.