[R] ggplot - plot with only legend?

[Pedro de Barros]

Dear R'ers,

I am trying to build a composite plot (with several plots in one 
figure). I have tried, but I cannot use facetting, as I need to 
customize each plot using grid.
Since all the plots are the same (with different data, but same 
layout and categories), I would like to have only one legend, that I 
would place in its own viewport, below all the other plots. My questions are
(a) is there is a way, in ggplot, to build a plot that is only the 
legend (no data), where the legend occupies the whole viewport;
(b) How can I change the layout of the legend (e.g. have them written 
side-by side, instead of over each other).

Thanks in advance,
Pedro