Given the equation of an ellipse in "center" form:

(x - h)2/a2 + (y - k)2/b2 = 1

...the center is (h, k) and the foci are the points (-c, 0) and (c, 0), where:

c2 = a2 - b2

Note: This assumes that the major axis is on the x-axis. If the major axis is on the y-axis, then switch "a" and "b".