See Valen’s reply above. Sony have produced / are producing /will produce (sorry, I can’t be more clear than that…) -a kit to add a hard drive to the PS2. The plate at the rear of the HD will also have an ethernet port and possibly others.
There was an article posted here on Amiga.org about it a few months ago. As for linking network games run on it to your Amiga/Mac/PC, et al, I remember thinking that this would work real well with Amiga’s Digital Enviroment, as soon as the appropriate translation layer was written…