Big question to the OP, if he/she still reads this thread:
How exactly did you get 7 Watts idle with Win 7, I mean what hardware/peripherals/cables were connected to the DN2800MT?
I have now installed a clean copy of Win7 SP1 Home with all the latest drivers (GPU, audio, chipset, LAN) from the Intel DN2800MT driver download page because I wanted to have some reference power readings to compare my Linux power readings to on my specific setup.
DN2800MT in mini-box M350 case
1x Samsung 1GB DDR3 8500 (1066Mhz) SoDIMM (I chose to go with the absolute minimum for this test on purpose)
1x Intel 311 mSATA SSD 20GB (Intel claims this SSD only uses 150mW when active, so next to nothing)ELV 87586
36VA power brick set to 12V
Watt meter: Profitec KD-302 (known to be very precise even at very low Wattage, usable range: 0.2-3600W)
When WIn7 is sitting idle at the desktop with 1 USB keyboard and 1 USB mouse connected, 1 Gige cable connected with idle link and a 17" LCD (1280x1024) connected via VGA I read 10.1 Watts
(nowhere near 7 Watts!)
If I disconnect the USB mouse and keyboard (with integrated mini USB hub), the power consumption drops to 9.7 Watts
Once Win7 switches the monitor into DPMS standby after about 10 minutes idle, the power consumption drops to 9.1 Watts
If I now detach the ethernet cable
, the power consumption drops to 7.7 Watts
I can't get the power consumption any lower than this with Win7. What made a big difference was disconnecting the ethernet cable, so I guess when the OP did his tests he also didn't have an ethernet cable connected.
In view of all this the Linux power readings weren't that bad at all, yes they were still higher but not 5-6 Watts higher as I was thinking based on the OP's power readings (7 Watts Win7 vs. my 12-13 Watts Linux).
Now once the Mageia 3.3 kernel package is available I will do the same tests with Mageia Linux.