[R] Square matrix plot

[Finocchiaro Giacomo]

Hi,

having a matrix where rows=n and cols=m, I calculated the spearman 
correlation values of the matrix, this generated a square matrix m x m.
Dose anyone knows how can I create a plot similar to this

http://bio.ifom-firc.it/User/finoc/ask.png ( produced with hierarchical 
cluster explorer)

using R? I would like to have a range of colors from green(-1) to 
red(+1)  proportional to the correlation value calculated. Thanks a lot. 
Regards

				Giacomo Finocchiaro