It has been a while since my last stay at OSxLatitude forums but if I remember correctly, I re-did the installation a few times with different strategies.
The 1st problem with this generation P4 chips is the lack of SSSE3 instructions, but this can be circumvented with the Nawcom ModCD and legacy kernel.
The second major problem is the onboard graphics, as they are not supported in SL. Of course, any supported gpu can be retrofitted.
Needed kernel flags:
legacy_kernel arch=i386 -legacy cpus=1
My suggestions for a install strategy:
1) Install 10.6.3 with ModCD, and install the bare minimum necessary kexts.
2) configure your bootloader of choice
3) Download 10.6.8 combo update and the legacy kernel for 10.6.8.
4) run the combo update but DO NOT LET IT REBOOT!
5) install the legacy kernell for 10.6.8 and then reboot
6) install non essential kexts such as audio and networking
7) success
Good luck!
-N