I've looked at the Ebay link and also looked at the AMD website. This confirmed what I thought. The 400MHz fsb was introduced with the Athlon XP3200+ cpu. The 2800 supports nothing faster than 333MHz as stated by others before me. The Ebay auction is misleading and you might like to report it to Ebay.
the only 400 fsb AMD cpu is the 3200+ and if ya believe AMD, it will be the only one as the are consentrating on athlon 64 cpu's and will not be making XP cpu's any more after the 3200+ run is finished, if it aint all ready.