Have you tried setting it manually, outside of the BIOS?

Here's the manual for your motherboard, in case you don't have it handy: ftp://ftp.asus.com.tw/pub/ASUS/mb/sl...f/p3bf-104.pdf

At the top of page 20, move the jumper JEN from 2-3 to 1-2.

Then, set up the DIP switch "DSW" according to the settings on pages 17-19. For your system, the settings should be as described in the table at the bottom of page 19:
1: ON
2: OFF
3: OFF
4: ON
5: OFF
6: OFF
7: OFF
8: OFF
9: OFF
10: ON

Obviously something is screwy here, and I disclaim all liability for you blowing up your system. But on the other hand, it's not like you couldn't replace the whole mainboard assembly for $50. :D

$50? I could probably buy two of them for that. I bet I've thrown away 10 P2/3 MBs in one month before <G>.

Well, I was assuming a slightly more modern Socket 478 / 775 system. You know, something that auto-configures itself. :D

Any luck with the manual configuration?