It is probably a Palomino core downclocked to 100Mhz FSB. As far as I know all Athlon XP's use 133MHz bus speed, not 100. You should be able to set it at 133MHz without problems. But wait for somebody else to confirm cause I am not completely sure. The RAM is DDR, right?
The multiplier is 10.5x because 10.5 x 100 = 1050MHz. I think you have the exact same CPU I do. Putting it at 133MHz will result in exactly 1.4GHz (AMD Athlon XP 1600+).
TheMajorMMX - Intel P200 MMX @ 225Mhz - V-Tech (PcPartner) Baby-AT mb w/ Intel Triton TX chipset - Nvidia Riva TNT2 M64 w/ 16MB - 256MB M-Tec SDRAM - Still running.....