[R] Creating error bars in scatterplot() function (cars-Package)

[philsen]

Dear list,
I am new to R and trying to create a grouped (four groups) scatter plot 
with error bars (only in y-direction) using the scatterplot() function 
from the car package.
The code I am using for plotting the scatter plot is:

scatterplot(a$s_profile~a$s_plot | a$group, data=a)

which gives me a nice grouped scatter plot. However I have no idea how 
to insert error bars. Using errbar() from the Hmisc Package gives some 
unwanted results, e.g. adding new points with an offset in xy(!?) even 
when specifying the xlim/ylim parameters.

Another problem is to move/orientate the plotted legend individually, is 
there any possibility?

I would appreciate your help in solving my problems.

Many thanks in advance,
Philip