THis is a cool question.
1) Use the point slope form to find the equation of the lines between two of the points (choose two points that when a line is drawn between them make a chord on the circle).
2) Use the midpoint of a line equation to find the midpoint of the line, then find the slope of the line that is perpendicular at that point and write an equation for it.
3) Then do the same thing for the other two points that form a chord on the circle.
4) Then set the two equations equal to each other and solve. The point where they meet is the circumcenter.