Ok, strange.

I can ping every machine in my network (wifi and wired) from the Pismo in wifi, and I can ping the Pismo from my MBP (in wifi too) and from other OS 9 wired machines.

From the Pismo I can connect to my MBP through AppleShare (by entering its IP in the Chooser) and it works, but I can't "see" other OS 9 machines in the AplleShare list, nor connect to them by entering their IP. And similarily, I can't see the Pismo from any other machine.