From http://live.gnome.org/Tomboy/Installing/Windows :
Instructions for installing a Tomboy Windows release
Upgrading from Tomboy 0.13.4 or earlier
- Uninstall Tomboy.
- Uninstall any existing versions of gtk-sharp you may have installed.
- Continue with Installation instructions.
Importing notes from Linux (optional)
- On your Linux box, copy all of the *.note files out of ~/.tomboy .
- On your Windows box, quit Tomboy.
- On your Windows box, copy all the *.note files from Linux into %APPDATA%\tomboy .
Thanks so much to Mike Kestner for working his ass off (on his own time) updating the gtk-sharp installers, making them easier to develop and build, and fixing the issues reported by Tomboy users. Apps like Tomboy, Banshee, and GNOME Do would simply not exist without all of his hard work.