You can use the AXP Barton's an the AMD760MP(X) chipsets without issue, providing you drop the FSB to 133MHz.
Whether the individual motherboard supports AthlonXP's is the only real factor preventing usage, and by and large almost all SMP boards have provides BIOS support for the AthlonXP.
FWIW, the AthlonMP 2800+ is also based on the Barton core clocked at 2.13GHz.