Now the machine was working fine with a modest over-clock from 3.1Ghz to 3.5Ghz, so really one would think that there is no point to updating the bios to support this chip. I thought, what the hell, I have a spare flash chip, ill have ago at it and see what happens.
I am proud to say that my board now recognizes my Phenom II X2 550 processor, here is my cpuz output to prove it

http://valid.canardpc.com/show_oc.php?id=595009
What I did was grab the latest bios from ASUS for my board, and the latest bios for the ASUS Crosshair II, which is a AM2 board with AM3 support. Using CBROM32 I extracted the AGESACPU.ROM (/GV3) from the Crosshair II board, checked it contained both AM2 and AM3 CPU strings, and after confirming this, used CBROM32 to insert it into the M2N32 bios.
After flashing the bios and rebooting, the chip is now detected... and as the CPU-Z output shows, I can now over-clock it to 3.75ghz, with a 250Mhz FSB on fan cooling alone. With water cooling I can now clock it to 4 ghz with a 260mhz FSB.
The updated bios is here:
http://www.spacevs.com/bios/M2N32-SLI-PREMIUM-1303-1.BIN