Tooltips (or similar) on a drawing area?

[Juha Nieminen <warp cs tut fi>]

  In an application I have a drawing area (created with
gtk_drawing_area_new()) where I draw circles and arrows between
them (ie. a graph).

  I would like to have tooltips on the circles, that is, when the mouse
goes over a circle, the program would popup a tooltip containing text
related to that circle (it's ok if the area where the tooltip pops up
is a square instead).
  The text can have several lines, so the tooltip should be able to show
several lines of text, not just one.

  What would be the best and easiest way of achieving this?

  (I am using gtk 1.2, but 2.x-exclusive answers are also ok. I could
upgrade.)

                                                        - Juha