[R] lattice graph/ panel.superpose / groups

[Karin]

Hello,
 
I am struggling with a lattice graph. 
I want to plot points and condition on a variable called 'Method'. 
For each conditional plot I have two subgroups, say: 'first'and 'second'.
I want to plot the points in a conditional graph with a different color or symbol for each subgroup. 
 
Moreover I want to calculate within each conditional graph limits of the points together (and thus not seperately) for the subgroups. I use this code:
 
xyplot(Y~X|methode,
 xlab="Average",
 ylab="Difference ",
 groups=SUBGROUP,
 pch=c(1,3),
 ylim=c(-0.1,0.1),
 key = list(space = "right",
  transparent = TRUE,
  points = list(pch = c(1, 3)),
  text = list(c("First", "Second"))),
 panel=panel.superpose,
 panel.groups=function(x,y,...){
   panel.xyplot(x,y,...);
   panel.abline(h=mean(y));
   panel.abline(h=mean(y)+1.96*sd(y)); 
   panel.abline(h=mean(y)-1.96*sd(y))
 },
 data=temp2)
 
However now I get lines for each subgroup within each graph, and that is not what I want. 
 
How can I give the points for the two different subgroups a different symbol, but lines that are for both subgroups together?
 
Thanks in advance,
 
Karin