Did you try putting it back in after you tried the old duron? It might be fine.... If the fsb thing was the issue. Mine was...

Yeah, tried that, no dice. Right now I'm running with my Duron in the new motherboard, and I'm sending the AthlonXP back to Newegg. I might swap the Athlon in one more time before I send 'er out just in case, but it definitely seems to be the CPU that's to blame.