Here is my situation...

Linksys 4 port router hooked up to a cable modem. 2 PC's (a & b both WinXP) are linked to the router, 1 other PC (c Win 2000Pro.) is linked to a 8 port hub with is connected to the router. PC's "a" and "b" can share files and "see" each other. PC "c" can connect to the Internet, but I cannot ping PC's "a" or "b" from "c". PC's "a" and "b" can ping PC "c". I have installed the same protocols on all machines. What could I be missing?? TIA!!