I would not guess that it is the root or a big part of your problem, but one potential confounder to consider as you troubleshoot is the ARP table on the 3Com. I think the SSII is smart enough to cache ARP entries associated to port/s, and if you are moving things like the Empeg around to different ports as you troubleshoot, the persistence of stale entries may add to unpredictable behavior that makes your troubleshooting more frustrating. There should be a way to clear ARP on the 3Com so that it forces broadcasts to refresh entries for Empeg, PC, etc.

Looking back at an earlier post, I see something I don't understand (apologies if someone already covered this) and have a few random questions:

1st computer is static 192.168.0.1 with ICS installed
(.....)
TheEmpeg(when set to DHCP) shows eth0 DHCP to be 192.168.0.1 which is the ICS machine and get assigned the next free IP on the network.

This last statement makes it sound as if the Empeg ultimately gets the same address assigned as the "1st computer running ICS". Am I reading that incorrectly? [edit: naw, I re-read that and see what you are saying]

What subnet mask is specified for these hosts? Have you tried all of this with a static IP/mask on the Empeg and on the PC running Emplode with only those 2 hosts on the network?

Also, it sounds like all link status lights on Linksys, 3Com, etc. are lighting up the way you expect, true?