you may already be familiar with the different cores of the athlonXP but just incase not below is a little info (by the way the info is by memory so it probably isnt 100% accurate)
1. athlonxp (palomino) comes in xp1500+ thru xp2200+ (these have not been made for awhile so it will be hard to find them in stores, but easy to find them forsale in the fs/ft forum
2. athlonxp (tbred A) not sure what speeds, this revision wasnt produced very long.. but i believe the very first xp2400+ chips were based on this core and probably a scattering of stuff between 1700+ up to the 2400+
3. athlonxp (tbred B) comes in xp1700+ to xp2700+ most anything bought today will be based on this core
4. athlonxp (barton) comes in xp2500+ to xp3200+ (this core is alot different the the other 3, and is much less likely to work on older boards)