biplot.princomp - changing score labels

Dear R helpers,

When producing a PCA biplot, vectors of environmental variables (as red 
arrows with labels) and scores of the observations (black labels 
(observation names)) are plotted by default. How can I change the 
graphical output? Let's say I would like that the scores are plottet 
only as symbols and not text. The only solution I found was this post in 
the help archive
http://tolstoy.newcastle.edu.au/R/e2/help/06/12/7298.html
suggesting "cheating" like:
 >biplot(test.pca, xlabs=c("0","0","0","0","0","0...
and using letters instead of symbols.
This works somehow, but I am still not able the change e.g. the colour 
or size of only the scores. Whatever I try to do with "col=...", 
"cex=..." and so on changes either all labels in the plot or none. Can 
someone tell me what is the trick to only modify either the 
environmental variables or the scores? Also e.g. the type of the arrow?

Thanks in advance,
Axel

Gravity is a habit that is hard to shake off.
Terry Pratchett