How to make label in multi plot

Dear R-Help,
As a reference about multi plot,
http://finzi.psych.upenn.edu/R/Rhelp02a/archive/48725.html

I want to know how can I make a label for each row.
I mean like,

                  ------------        -------------      --------------
                 |            |       |            |      |            |
Group A     |   plot1  |       |  plot 2  |      |  plot 3  |       
                 |            |       |            |      |            |
                 -------------        -------------      --------------

                                      -------------
                                      |            |
Group B                          |  plot 4  |
                                      |            |
                                      -------------

I  would be very happy if anyone could help me.
Thank you very much in advance.
Sincerely,
Muhammad Subianto