@Rd31: Are you sure you're using the mobi version on your Kindle? I'm not sure, but that vaguely sounds like you're trying to display a raw HTML file without proper styling, and that ends up using the Mono font...
@irha: No idea, don't use Windows
. You might try take a look at the Documentation/usb/linux.inf file of a recent Linux kernel, that may (or not) be of some help. The few things that seems to come out of this is that Windows' USB & RNDIS stack is utter crap. So, if it kills a kitten or crash horribly, you'll know why ;o).