All the DIP switches should normally be set OFF, and jumper JEN (which is above the front end of the ISA slot) should be set to cover pins 2 and 3.
This would let the BIOS control everything; most importantly the CPU core voltage.
If you really want to, you can give up easy control over that core voltage and be able to set the FSB and AGP divider with the DIP switches. If you want to alter the core voltage in this case, you'll have to paint some CPU contacts with nail polish.
Why do you think you want to do this?
edit: I may have been too hasty about the vcore control; there is a recent beta 1006.004 BIOS which may allow it. I don't know of any electronic reason why not, though I've never closely inspected the P3V4X's traces.
