I have to use the boot with one CPU trick in order to get Leopard to boot correctly.

Since I want to use Parallels in Mac OSX, I wanted to know if there was a way to activate both processors once the OS has loaded. I'm sure that this would improve performance during my daily usage. Thanks

I'm not sure which P105 you've got, but with mine I can use both cores of my processor just fine. I used iAtkos to install a mostly vanilla install, then updated to 10.5.5. Not sure what your problem is, but with me it was a matter of fixing my graphics. Until that was fixed, I could not use both cores. Using GFX Strings, I was able to get great graphics performance, and use both cores. Also, my hackintosh runs much faster with the stock kernel.