Hi Nick,
The answer depends on the version of Excel you are using:
2003 or earlier - Highlight all rows you are interested in by dragging
through the row numbers. Let's assume you highlight from row 1 down to row
28, starting in row 1.
Choose Format, Conditional Formatting, and choose Formula is from the first
drop down.
In the next box enter the formula =COUNTA(1:1)=0
Click Format and set whatever you want.