I've been working on an interface to easily connection up Director and the Gameboy Advance, allowing the GBA to act as a joystick to a Director interface, as well as to transfer data between the two entitites. This would allow the GBA to send/grab data online, particularly for an attempt I'm making of adapting the Abstract Machine Game designer for the Gameboy. So far I've got Director talking to the Gameboy Advance and sending data back and forth. But my protocol is a little buggy and I sometimes (in particular instances) don't perfectly map activity on the Gameboy from within Director. I think it's the way I set up my bitmasks that screwed me up, I'm going to have to start all over, I think.
I've got far more information on this over at the PLAY+MOBILE website, although it's in French (sorry!). But there are more links for you to work off of. I've been using an FTDI chip which allows me to plug the Gameboy Advance directly into the USB port of and Mac or PC. I could also plug into Linux, but since Director doesn't run on Linux, it's sort of a moot point for me right now.