[R] working with groups of labels?

[Phillip Porter]

Good Morning,
I have a graph with groups of variables.  I have include the group 
names as variables so that I can have them positioned correctly. 
Unfortunately this means that the group names have to follow all of 
the same rules as the variables within the groups.  I would rather 
have those group names left justified and bolded.

I know that I can do this in an mtext() function using font=2 and 
adj=0, but I can never get the labels lined up exactly right.

Is there a simpler way of getting one group of labels right justified 
and another group of labels left justified and still have them all 
automatically positioned correctly?

Thanks,
Phillip