I've got nearly the same board as yours, an A8N32-SLI Deluxe and have a X2 3800+ working without any problems on IDE drive.

Firstly make sure you hvae the latest BIOS. Then turn off all the unwanted stuff like sata ports and parallel ports etc that arent being used.

After you install Leo you will need to make the partition active and bootable. There is a guide in the wiki on how to do this. the b0 erro just means you're parition isn;t active. Use a tool like acronis from hirens boot cd or another tool like diskpart in windows to mark the partition active outside of osx. Goodluck.