Jax, to turn off SPLIT mode, simply load up OS3.9 or 3.1 (which ever you use) and execute the ATA3.driver file AFTER the OS has been loaded. You can do this by either loading the OS from an emergency disk, or even from another hard drive, and then opening shell command prompt and typing ATA3.driver (assuming that the file is either in C: or you are positioned to the same directory where ATA3.driver is located).
Now that you've executed the driver, enter ATA3Prefs program and viola! You can change the SPLIT option to NO SPLIT. Click on USE (don't SAVE at this point) and after you exit ATA3Prefs, fire up HDToolBox and partition your hard drive as you please (no more SPLIT crap)... then reboot, and you're all set. :-)
