You need to boot into OS X (which works currently with only 1 core active) and run fassl's DSDT Patcher to generate a patched dsdt.aml file....

A Terminal window will open......press any key to continue.....when you see

CODE
Which OS to emulate? [0=Darwin,1=WinXP, 2=WinVista]

choose 0 to emulate Darwin......

The dsdt.aml file you generate will be placed in the DSDT_Patcher1.0.1e directory/folder and should be renamed to DSDT.aml and then copied to the /Extra directory that you will see after installing Chameleon 2.0RC1 using the Chameleon 2.0 RC1 installer......

There is no risk to your BIOS AFAIK because the Chameleon bootloader loads the modded DSDT.aml file in the boot directory i.e. / directory over the DSDT file loaded from the BIOS.....

go in to the extray folder created by chameleon bootloader and the com.apple.Boot.plist open it with textmate and where you see make it say 4 if it does not cpus=4 this should fix every thing