[R] indicating significant differences in boxplots

[Sebastian Merz]

Hi all!

Writing a paper using a lot of boxplots I was asked to mark the
significant differences between plotted groups using "stars on
top". 

These stars are found freqeuntly in medical papers and printed
above boxplots when there is a significant difference (usually using a
bar to indicate which groups are meant if there are more then two in a
plot). 

I was able to calculate whatever test, check the significance and
depending on it to put a star (written with text-function) between
two groups in a boxplot. But I was not
able to make the text between two groups apear above the actual
plotting region nor to draw a simple line, indicating which plots are
meant. Also this solution seems to more of a hack then actual
programming.

Is there a better way to solve this issue? Any ideas where
to look?

I hope I haven been clear and thank you for your effort,
S. Merz