Boxplot width

Hi there,

assume that you have data with different sampling like

d1 <- rnorm(100)
d2 <- rnorm(150)

now, I'd like to create two boxplots in one graph but each plot located at the 
sampling number at the x-axis. This, I can do with "at"

l <- list(d1,d2)
boxplot(l, at=c(length(d1), length(d2)), xlim=c(0,200) )

but both plots are very thin and I'd like to increase the width of the plot.
I tried "width" but probably I do it wrong.

Can anybody help me?

Antje