0d:00.0 Ethernet controller: Intel Corporation 82573E Gigabit Ethernet Controller (Copper) (rev 03)
http://download.intel.com/design/network/specupdt/82573.pdf 17 ASPM/Jumbo Frames Disabled Due to Early Receive Threshold Overrun Buffer Status: Intel does not plan to resolve this erratum in the 82573 Gigabit Ethernet Controller. Jumbo frames is not supported in 82573E/V& is supported with the workaround above in 82573L.
Interestingly, I somewhere got the same PDF (from the intel site) that required a password -- and didn't investigate further on your link. Now, out of curiosity, I did...
You'll have to use different hardware. The chipset you've got has a bug, and jumbo frame support is disabled as a result.
...and yes, you're right.
I'm amused about PeeCee hardware (sorry, only half of a pun intended)... There's those two NICs on board of a *server* grade machine, a 82573E and a 82573L. One of them is just *broken* (see above).
Cheers,
Timo