It actually looks like there may be some software for uploading stuff to the Garmin unit. But if you want to create routes and stuff, I think you're stuck with Garmin.
Runs Debian on my servers, Gentoo on my AMD64 workstation, and Kubuntu on my laptop and on my girlfriends machine. I've got an old dedicated WindowsXP box with a KVM switch - but it's mainly turned off, and the laptop dual boots into WinXP