R help - Jan 2008 - Identifying x, y coordinates from periodogram generated by spec.pgram

I would like to identify the x,y coordinates in a plot of the periodogram

spec.pgram(a, taper=0, log="no")

I have tried the identify() function to no avail

I have also tried to pass the periodogram over to rggobi

e<-plot.spec(spec.pgram(a, taper=0, log="no"))
ggobi(e)

to no avail

I need to identify the predominant frequencies so that I can work back
to the time of recurrence in minutes.  I don't necessarily need a
interactive
graphical solution (although this may be easier).
thanks

-- 
Let's not spend our time and resources thinking about things that are
so little or so large that all they really do for us is puff us up and
make us feel like gods.  We are mammals, and have not exhausted the
annoying little problems of being mammals.

								-K. Mullis