figure with inset

I am trying to plot a figure within a figure (an inset that shows a closeup of
part of the data set). I have searched R-help and other sources but not found a
solution.

What I would like to do is

(1) produce a plot
(2) specify a window that will be used for the next plot (in inches or using the
coordinate system of the plot produced in (1)
(3) overlay a new plot in the window specified under (2)

The result would be:

+----------------------+
|                      |
| first plot           |
|       +--------+     |
|       | inset  |     |
|       +--------+     |
|                      |
+----------------------+

Thank you for your help

Pascal