R help - Mar 2006 - highlight an area below a line

Hi,

if I plot a normal distribution like this:

d<-density(rnorm(10000))
plot(d)

how can I highlight the area below the graph in a certain interval,
say x=1,2?  I understand that I should use polygon, but I have not
found the right way to give the result that I want.

Thanks a lot!

Georg