Sure you can.
I have my osx86 10.5.6 100% working. Same Board, same stuff.
First, u'll need to disable the Hyperthreading technology (bios), or you'll get a continuous kernel crash.
How it worked for me:
Things U'll need
#DVD TOH RC2 SSE2/SSE3 (there ain't a lot of people sharing this torrent, but worth waitting)
#Combo Update 10.5.6 (at apple.com)
#Combined Post Patch (Extract it to a pen drive - MAKE SURE THE DRIVE AND THE FOLDER U'LL EXTRACT IT DOEN'ST HAVE SPACES IN THEIR NAMES.)
#VOODOO KERNEL XNU FINAL RELEASE DMG (wich includes the system.kext from 10.5.5)
#seatbel.kext from 10.5.5
#A COMPATIBLE VIDEO CARD (Search the forum to see if u'll able. my card is a Geforce 6200 256MB, great card for osx86)
#stock APPLESMBIOS.kext and APPLESMBIOSEFI.kext
#efistudio, osx86tools, uinstaller (Great tools to keep your system cool)
Install it following this steps
1.Boot from dvd (about 6 minutes)
2.Get your partition done with Disk Utility (MBR, HFS+ JOURNALED)
3.Install Mac OS X (uncheck the printer's driver and language option)(this DVD includes all the languages available)
4.When the installation is over, reboot again from the DVD
5.Go to Terminal from the utilities menu
navigate to the folder u've saved the combined_post_patch
"cd /volumes/the_name_of_your_pendrive_/combined_post_patch" (if, for example, u've extracted it to the root folder of your pen drive)
run the command= "./patch.sh the_name_of_your_mac_partition"
Say YES to everything BUT the ask about VIDEO CARD RESOLUTION.
If u say Y to the video card resolution, it may not boot. Just redo the post_patch again and say no to it. It's the last question of the post_patch.
6. Reboot, remove the dvd from drive and configure your mac. Follow the screen instructions.
7. Install the video kext. For me, it's the titan.kext. Serach yours at the forums.
8. Open disk utility and repair permissions.
9. reboot and let's go to the 10.5.6 update.
Install the voodoo kernel from the installer (to do it manually, make sure u have the system.kext from 10.5.5).
Open The EFISTUDIO and add the ETHERNET on DEVICES.
Open the OS86TOOLS and install the following kexts (SAY NO TO REBOOT ASK AFTER INSTALLATION)
#Seatbelt.kext from 10.5.5 (this will prevent the the 10.5.6 system to crash everytime u try to mount a dmg or disk image).
#APPLESMBIOS.kext (the stock one, from original LEOPARD)
Now remove the Extensions Cache and Touch Extensions with OSX86TOOLS.
Now let's update it.
Run the 10.5.6 Combo Update (about 600MB) (BUT DON'T REBOOT)
wait for it to install. (if anything goes wrong and u get a kernel crash, don't worry. Make sure u didn't forget any of the steps above and try it again.
After complete the installation, Reinstall the following kexts with OSX86TOOLS (Do not reboot)
#system.kext from 10.5.5 (if you don't know where to find it, just reinstall the Voodoo package)
#seatbelt.kext from 10.5.5
Now reboot, REPAIR PERMISSIONS and enjoy a 100% working 10.5.6. Evertyhing works great. The sound get 2 channel out (line out doesn't work, but u can use the jack right above the speaker out. them both works like a charm. Microphone works great. If you have any trouble, configure it with AUDIO MIDI Setup utility.
Depending on your system's ammount of RAM memory, you can run every application u wish to. I run with no problems the CS4 Master Collection, the Final Cut Studio 2.0, the iLife '09 and iWork '09, Maya 2009 and so much more.
Now keep your system updated with software update and enjoy it!