Axis-question

Hi there,

I was wondering wether it's possible to generate an axis with groups (like in 
Excel).

So that you can have something like this as x-axis (for example for the 
levelplot-method of the lattice package):

---------------------------------------------------
| X1 | X2 | X3 | X1 | X2 | X3 | X1 | ...
| group1       | group2       | group3  ...
..
..
..

I hope you understand what I'm looking for?