[R] Lattice graphics: adding lines to a plot

[Matthew Walker]

I am trying to use the Lattice package to produce the same result as I 
can with the base graphics.

With base graphics I can type:

x <- 1:100
y <- x+rnorm(length(x))
g <- lm( y ~ x )
model.y <- g$coef[1]+g$coef[2]*x

plot(x,y)   # a plot of the data
lines( x, model.y )   # a plot of the model, superimposed on the first plot


With Lattice graphics I've got this far:

library(lattice)
plot1 <- xyplot(y ~ x)
plot2 <- xyplot(model.y ~ x, panel = function(x, y) { llines(x=x, y=y) })
print(plot1, more=TRUE, position=c(0,0.5,1,1))
print(plot2, position=c(0,0,1,0.5))

But this just produces two graphs, one above the other.  How do I 
overlay them?  What should I be doing in order to get the same result as 
with the base graphics?

Thank you for your thoughts,

Matthew Walker