p35-ds4 10.5.6 10.5.7 vanilla boot reset

[tham50]

hi,

i know it's kinda classic but i got the nasty reboot thing when using the vanilla kernel. chameleon comes up, kernel loads and right after the kexts are loaded and the resolution change should happen i get a happy reboot/reset
tried 10.5.6 and 10.5.7 kernels.

p35-ds4
c2d e6320
8800gts
sata disk

the funny thing is i can boot snow leopard just fine (using its vanilla kernel).
so what's the matter with 10.5?

any hints are welcome