Like rob_rd I have 'the low id' problem. The Netgear WGR614 router has port forwarding of 4662, 4665 and 4672 set for 192.168.1.3 which is this iMac running OS 10.4. The ports are as set in aMule Preferences. The Apple firewall is off.
The internet conection is bigpond.net.au ADSL and, as far as I am aware, they do not do any type of port blocking. Or if they do, they don't admit it!