Eh, basic circle script equations when you want to solve for x and y positions:
PHP Code:
x = centerx + r*cos(A);
y = centery + r*sin(A);
//Obviously center x and center y would be your coordinates.
//A stands for alpha and should basically just be increased by .05 each run
//through, basically 'a += .05;'
//And r stands for the radius of your circle