windows mobile center driver didn't work for me either.
But I found an other solution, happily xerox provides a RNDIS driver to service their copy machines, it's called xerox service port.
download NDIS Driver Xerox
it's a selfextracting exe, extract and and instert kindle usb cable,
when it ask for driver point to XeroxServicePort.inf in xp/vista driver
config network adapter ip4 settings to ip:192.168.2.1 subnet:255.255.255.0
afterwards telnet (eg. putty) to 192.168.2.2
here it goes
sometimes it stucks and the adapter is deactivated and does't get activated again,
since it's windows reboots helps