Import folders from Thunderbird to gmail?

Actually, I was able to successfully create a folder and a subfolder on some random account using Mail on Snow Leopard, populate them with a few messages and then export the hole structure on my Gmail account by just drag & drop.

The result is the expected messages with labels:

You first need to find someone with a mac and Mail, and then you can use Eudora Mailbox Cleaner to import from Thunderbird into Mail. I know this isn't quite straightforward, but it seems to work at least.