The Athlon XP had 4 core revisions, palomino, thoroughbred A, thoroughbred B and Barton.
The sempron can use one of 2 cores, either a cut down version of the Athlon64 core or the thoroughbred core from the old althon XP. Your one uses the thoroughbred core.
My point being that the sempron IS the AthlonXP. (Although your Athlon XP is still faster because it has more L2 cache).