Quite often routers depend on a specific version of Java, or worse, jscript, which is Microsoft's proprietary version of Java script. Did you use the PC or the MacBook to manage the router? The Java thing could be the problem here. You also must open the ports in the OS X firewall-have you done that?
And check this forum back about six months or so-we had a number of threads on iChat and what ports it needed to have open.