Silly question, but you have verified that your cable is correct? Not using a crossover post on the cabletron?

(if you are getting it to respond to the management screen, i'd have to say the wiring is correct enough)...

That's wierd. The only thing I can think of was a similar problem on our HP switches... Before upgrading their firmware, any 3com card capable of 100Mbs operation would perform like [censored]. Max throughput of about 1-2 k per second. Even if you forced both the card and the switch into 10hd, it tried to run 100FD. Put a 100mbs switch (cheap, $60 variety) between, and it would operate 100mbs no problem, getting 7000Kps no problem. Of course, the majority of these were in Dell Optiplexes, integrated. Pain in the ass to replace an integrated net card.

Found an updated firmware about 2 weeks later, and applied it to the HP's... Everything has been cheery since.

Not saying this is your problem, as you've tried different hubs/switches... but it does seem VERY strange that the empeg ONLY works on that hub.

Have you tried putting both the empeg and your PC on the linksys 10/100, taking the 3com out of the equation?