The P5KD 0403 bios is up on

ftp://ftp.asus.com.tw/pub/ASUS/mb/so.../P5K%20Deluxe/

I successfully flashed to 0403 from 0311. On the initial boot I had a check sum F1 message but all the boots since have been successful after I set my defaults.

The one change that I've noticed is on the JumperFree Configurations page. I believe it's the much awaited option:

FSB Strap to North Bridge [Auto], 200MHz, 266MHz, 333Mhz

Click image for larger version.  Name: FSB Strap.jpg  Views: 1085  Size: 90.6 KB  ID: 60769

At this point I'm not sure what this change means.