Greetings! I'm writing this post in order to inform you guys that
there is a fully working,almost rock stable version of Mac OS on my computer. This is my hardware list:
Motherboard: Supermicro H8DAE-2 with nVidia MCP55 Pro chipset which supports up to two Six-Core AMD Opteron 2000/8000 processors
Super Micro Computer, Inc. - Aplus Products | Motherboards | H8DAE-2
Processor: 1x Opteron 8214 (for the time being) :-)
Ram: 4 GB Samsung DDR2 667 Registered ECC Unbuffered
Graphics Card: Nvidia 9400 GT
I also have two SATA hard disks, 120 GB and 640GB , a Sony IDE DVD reader and an Optiarc DVD Recorder.

I was trying to install 10.5.7 iATKOS but without success.The installer was booting fine, the disk utility was working but I was always getting "kernel panic" after about five to ten minutes at "Installing" screen. So I couldn't manage to install this at all!
My next attempt was with iDeneb 10.5.5. The installation was smooth, but my system couldn't boot (I remember that it was always freezing after loading my dual ethernet cards, but without an error message) So no boot.

My last and successful effort was with XXX 10.5.6 OS. Everything went smooth with the first installation!! The system boot is very nice and quick -it takes only 68 seconds to boot! :-D The OS runs flawlessly, it is very stable. (Untill now) the only problem is a hesitation and a time waste wherever I want to change the screen resolution but i really don't care about it!
Safari,iTunes,Firefox,Opera,Openoffice,Vlc,Transmi ssion,Proteus -everything rocks!
I have some screenshots too but I don't know how to upload them.
Thank you XXX team! :-)

thx for sharing the info george, check here to get full support for your video

btw can you post how you get it working, surely will help other members

Ok! Here are my selections from the XXX 10.5.6 installation CD:
*Essential System Software -> ALL
*X11 -> ALL
*Optional Bootloader -> PCEFI_V9.0
*System Kexts->Essential System Kexts ->ALL
*Optional Kernel -> 9.5.0 Voodoo XNU
*Chipset Support-> AppleNForceATA (or AppleNForceATAtest)
*Network Drivers-> nForceLan ethernet
*Tools -> All

Note:I haven't selected any audio kext, because I'm using voodooHDA.kext 2.2 (without prefpane,but both are ok).

I updated my installation from 10.5.6 to 10.5.7 using apple combo update. I was an easy procedure, all I had to do was:
1) backup my voodoo 9.5 kernel
2) install the Voodoo based XNU 9.7 kernel by qoopz (I named it voodoo97 and NOT mach_kernel)
3) run the combo updater
4) restart using "voodoo97" kernel (2 times)
5) delete AppleHDA.kext, AppleIntelCPUPowerManagement.kext Rename "voodoo97" kernel as "mach_kernel"
6) Run Disk Utility / Repair permissions / Reboot
DONE!

OK,Here are 2 screenshots from my system profiler:

Hello again! I'm writing again because I want to make some corrections on my fist post.
First of all, iATKOS 10.5.7 DOES work on my pc. My bios settings were wrong and I had kernel panics after customizing the installation.
Here are my selected Software/Kexts/Patches from the installer:
*Iatkos v7 Main System
*Bootloader -> Chameleon v2
*X86 Patches -> Extra Directory
*X86 Patches -> DSDT
*X86 Patches -> Decrypters (Apple Decrypt and dsmos)
*Kernel -> 9.7.0 Kernel Voodoo
*X86 Patches -> Disabler
*Drivers -> VGA -> nVidia -> EFI string for nVidia -> DVI/VGA
*System -> SATA/IDE -> nForce SATA/IDE
*System->PS/2 mouse/keyboard -> Apple PS/2 Driver
Notes:
1) I installed VoodooHDA-0.2.2 after installation so no need to select audio driver. There is an older VoodooHDA kext available inside the DVD which is working ok but I haven't tested it extensively
2) The NForce Ethernet kext (focedeth.kext is its name inside the Extensions folder) cannot work with my dual onboard lan.... when the mac os boots, the adapter's leds turn completely off and the interfaces aren't working. So I installed the nForceLAN.kext from a backup of my older XXX 10.5.6->10.5.7 installation in order to get EVERYTHING to work ok!

CONCLUSIONS/TIPS:
I figured out that bios adjustments are VERY IMPORTANT in order to make mac os run really stable.If the adjustments are wrong, you cannot even install mac os! This board has tons of adjustments inside bios's menus and that's one of the reasons I truly love it! I believe I have found the optimal adjustments and now the mac os is running REALLY STABLE! No crashes at all, no Kernel Panics at all, no hesitation at all.... everything is in perfect working order! This must be definitely one of the best mainboards for most operating systems out there, including leopard of course (I am also using linux-mostly slackware, solaris express community edition-lots of builds, winXP 32&64 bit, FreeBSD and OpenBSD)
The only thing that I really don't know if it's working is the "Sleep mode" and that's because I've never use it and never cared about it in any os. I also noticed that windows XP 32 bit (without service pack, but with vmtools installed), is running slow through Vmware Fusion 2.0.2. I haven't tried any other version of Vmware fusion, and I haven't installed Fusion on my iAtkos 10.5.7 installation yet. I also haven't try any other os through fusion.
I will post some photos with my bios settings within the next days. I may also post some screenshots from my new 10.5.7 installation.