levelplot add line

Deepayan,

Thanks for the quick response.  Just to make sure I understand, let me
explain in a bit more detail what I am trying to do.

I have created a levelplot (with contour lines and colored regions), and
what I am trying to figure out now is how to add a series of horizontal
lines across the levelplot and also assign values or labels to the lines
on the alternative y-axis.  Would I do this with the route you suggest
below?

For adding the lines, yes. Take a look at ?panel.functions and ?llines.

I'm not sure what you mean by 'assign values or labels to the lines on the 
alternative y-axis'. As a general rule, panel regions are 'clipped', i.e., 
any attempt by the panel function to draw outside the panel has no effect. 
This can be overridden by with lset(list(clip = list(panel = FALSE))), but 
I wouldn't recommend using it unless you know what you are doing.

Deepayan