nForce3 Ultra mobo memory hole problem

[macbrush]

I have 4GB installed, so I thought i better turned on S/W memory hole. After that my system become very unstable, freezes at random, so I began investigate. The problem is that if I have S/W memory hole turned on, whenever the OS access near 4GB region, it freezes up.

 

Then I use memtest to test out the system. With memory hole enabled, I get all sorts of errors after 4076MB, but testing individual piece of RAM proved they're good, testing individual slot, and they're also good.

 

Another problem is that if I disabled memory hole, forcedeth.kext refuses to load, so I have to give up 1000Base/T, and go back to the good old 3Com 3c905C.

 

Is there a way for OS X to see 4GB without turning on memory hole? Is it a known problem with nForce3 Ultra mobo? Any suggestions?

 

Mobo: nForce3 Ultra 250

CPU: Athlon64 X2 4200+

RAM: 4 X 1GB DDR4200

OS: Tubgirl 10.4.10 with ToH kernel

 

Thank you for any ideas in advance.

[macbrush]

BTW, is there a kernel boot option that could limit the memory the kernel could access? Something like mem=3900MB?

 

Thanks