. . . after making sure that the only copy of dsdt.aml on your ION 330 is the one I've provided, installed to /Extra; with the 10.5.6 kernel you should be able to enable hyperthreading in the BIOS & see this:
. . & this:
. . . FWIW my Geekbench32 'score' went from 1250~ish with 2 cores (rather worse than a first-gen single-core Intel Mac min) to 1600~ish with 2+2 'cores' (rather better)
This last install, I tried an iPC build 10.5.6 with your DSDT file and there is still no go for the 2 cores. Even with my O.C. param's set the same as yours (Manual, 167mhz), I still ahve to use the CPU's=1 flag to get a boot out of it.
See my CPU-X output below. Dont know why, but my values do NOT match yours in the spped categories. Any chance you will put your ORIGINAL 2GB of ram back in your system and try with a DSDT file config'd for 2GB, I would like to put my RAM theory to rest once and for all. Also, is the 4GB of ram you are using DDR2 or DDR3? Thanks!