[R] levelplot in combination with xyplot

[Eelke Folmer]

With levelplot I would like to combine fitted values and "raw" values in 
one plot. The surface should be based on fitted values and on top of 
those I would like distinguisable points based on the raw data with a 
colorscheme the same as the surface.

# raw data
x1 = rep(1:10, times = 10)
x2 = rep(1:10, each = 10)
y  = 2 + (x1+rnorm(100, mean=0, sd=4)) + (x2+rnorm(100, mean=0, sd=2))
levelplot(y~x1+x2)
# predicted data
fit = lm(y ~ x1 + x2)
x1.mesh = do.breaks(range(x1), 50)
x2.mesh = do.breaks(range(x2), 50)
grid    = expand.grid(x1 = x1.mesh, x2 = x2.mesh)
grid[["fit"]] = predict(fit, newdata=grid)
levelplot(fit ~ x1 + x2, data=grid)

So, instead of plotting both levelplots (like here) I want the first on 
top of the second. I tried a bunch of things (including panel.xyplot 
within panel) but am now doubting whether it is possible?
Thanks in advance,
Eelke