I dont know maybe something changed between 10.5.2 and 10.5.6 in Intel 950 support, if it boots all the way to the desktop but it doesnt work there that would be my first guess.
Only other idea would be checking if your USB bus works good, I got something similar when the USB reset was not being done properly (though on different hardware), try disabling USB Storage and Legacy support in the BIOS or use Chameleon2's EHCI/UCHI Reset options.