Finally managed to get sleep (and therefore both cores) working on an Inspiron 9400 with an NVidia GeForce Go 9700 GS.
After much tinkering and many reinstalls, I was able to isolate the video card as the weakest link. Sleep WILL NOT work with Titan or Natit, even if I'm using the 10.4.8 GeForce kexts; using NVidiaEFI 1.0.2 with the 10.4.8 kexts works beautifully, however. Here is the final journey I took to get it working, as far as I can recall:
1) Installed JaS SSE2/SSE3 DVD with Semthem 10.4.8 kernel.
2) Installed mobility.kext (found on this forum) and patched AppleHDA.kext
3) Installed JaS 10.4.9 upgrade combo package
4) Turned SafeSleep off with 'sudo pmset -a hibernatemode 0'
5) Turned off 'Enable disk to sleep when possible' (or whatever) and changed Display Sleep to 'Never' in Energy Settings
6) Installed NVidiaEFI 1.0.2 kext and removed Titan.kext
7) Fixed relevant permissions
8) Reboot and used kernel flags 'cpus=2 fsb=166 fn=1' (if I do not specify 'fn=x' then I get thrown into single user mode during boot)
9) Use Apple menu to enter sleep mode after OS X is up and running, and the machine goes into S3 state without any issues. Upon wake, both cores are functioning.
'uname -a' confirms I am using the 10.4.9 netkas HPET kernel and I did double-check to make certain that the GeForce/NV40 kexts were still the same version as the 10.4.8 DVD. I also replaced IOPCIFamily.kext and IOPCCardFamily.kext with ones I found in a random thread at one point (attached as 'Extensions.zip', but not the same 'Extensions.zip' available in the 'Useful Files' thread), but as I later re-replaced them with the original versions off the JaS DVD, I do not believe they played an integral role in getting sleep to work.
As for BIOS settings, I'm using the latest A08 and I have NX enabled, Virtualization/Vanderpool enabled, SpeedStep enabled, and both cores enabled (obviously).
Hopefully this will help some of you who are having issues with entering sleep mode and using similar video devices. If not, let me know and I will have a trawl through my Extensions folder to see if there's anything else I messed about with and forgot (it was about the 8th reinstall, so details tend to get a bit mixed up when you're not actually expecting things to work on that particular attempt!)
Best of luck to all! (Now who's going to solve the subwoofer issue so I can have a fully working machine... ?

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I tried so search for the mobility.kext in this forum but failed, can you please put it here, thanks a lot.