Indeed.
THe prucedure is simple:
You need:
1x PC with Ethernet card
1x GC w/BBA
1x ethernet cross cable between GC and PC
1x Phantasy Star Online
Now, what you do is go to the web browser in Phantasy Star, you must set the settings so it believes your PC is the server it's supposed to connect to, then you load up a little "update" to the GC, a small program that enables you to stream disc that through the BBA.
Ofcourse, every game needs it's own speed config and stuff for this streaming, stream the data too fast and stuff like music and FMVs will be problematic, same goes for streaming too slow, but streaming too slow also affects gameplay... like in Metroid Prime.
Now, I've never tried this at all, but I know the ABC (+the entire rest of the alphabet)
The docs for this covers everything on how to do everything!
You're looking at old stuff!