[OS X TeX] diagonal lines in tables

[Kyle Johnson]

I am building a table with horizontal and vertical rules to produce  
cells into which values will be entered (by hand, by the students to  
which this table will be presented). Some of those cells should be  
ignored (as the values are irrelevant). I would like to put a diagonal  
line through those cells. I have not found a way of doing that. Is  
there?

Kyle