I have a center point up and away from a point on a diagonal line but for some reason I can't get the circle to pass through the point on the diagonal line it keeps drawing the circle tangent to the diagonal line.
One of your Esnaps is likely screwy. Draw a line, any ol' line, from that point you want the circle to go through on the diagonal line, then use the End of the line or Intersection snap to set the circle radius.
Oh, it just occurred to me, a "Node" is a created point. You have to make it. DS won't pick up on intersections and ends as "nodes" like some drafting programs do. Maybe that is what is messing you up.