Hey.
Just installed my P5Q with OSX86. Everything works like a charm.
1. Download iPC OSx86 10.5.6 Universal PPF5 (Final) and burn to DVD.
2. Patch BIOS with this file:
http://ve1.jkit.nl/~dignus/bios_p5q.zip
3. Put harddisks in AHCI mode under "storage configuration" in the bios
4. Boot DVD, install to your disk and add the following drivers: drivers -> chipset -> Both ICH**** drivers
5. It'll boot into OS X when you're done, download this zip to a USB stick:
http://ve1.jkit.nl/~dignus/drivers_p5q.zip.
6. Put the stuck in the osx86 machine, open up Kext Helper B7 and put the 4 kext files into it, enter your pass and click easy install. Reboot .. and you're done! You have to change the default output for sound btw.
Updating with the iDeneb combo updater to 10.5.7 works like a charm, although first time after update you have to boot with the -v switch.