Multi-Platform Encrypted Disk Image Formats?

LockedDisk asks: I'm looking at an application that will use USB flash devices to distribute information that, while not "top-secret", is sensitive enough that I'd prefer not to distribute it in plaintext. It'll be accessed from multiple platforms by the users who get them. What I'm hoping to find is a tool to build encrypted disk images that can be mounted on Windows, MacOS X, and hopefully Linux as well. What I'd do in distributing these is put the encrypted image on the device, with mounters already on the thumb drive. Users would be able to simply use the right mounter for their platform. For instance, I know PGPdisk would support the multi-platform part, but the mounter doesn't look like it's very well-suited to what I'm looking for. Mac .DMG files can be encrypted, but I know of no way to mount them on any other platform. Any ideas, folks?"