I was able to follow these instructions and get a root access from windows 7 64 bit:
http://docwiki.gumstix.org/Windows_XP_usbnet
I was then stuck not being able to get internet access from kindle. I did enable sharing with my wifi, so it is not that. I can't ping google.com (even by ip) and I can't even start the store (it asks me to turn on wireless, and if I answer "no", it doesn't even start).
I actually tried to follow instructions from
http://jyavariousideas.blogspot.com/...hering_27.html, but some of these might be out of day (e.g., the /etc/init.d/usbnet file is already created by the hack install, though the contents appear to be different). I don't know where I can find the up to date instructions that go along with the latest usbnet install.
BTW, I also tried this on a mac, which had the same issue. I was able to ssh in, but not connect to internet from kindle.