[R] 'beside' option for boxplots

[Malcolm Ryan]

Is there any way to get a boxplot of several data sets beside one  
another on the same graph, as there is for barplot?

If I do:

d1 <- data.frame(a = c(rep(1:3, each = 3)), b = c(1:9))
d2 <- data.frame(a = c(rep(1:3, each = 3)), b = c(9:1))
boxplot(d1$b ~ d1$a)
boxplot(d2$b ~ d2$a, add=T)

It will show the two datasets on the one graph, but the middle point  
will overlap.

What I want is a layout more like:

barplot(t(matrix(c(d1$b, d2$b), ncol=2)), beside=T)

only showing the boxes from the plot above instead of bars.

Can this be done?

Malcolm