Is there any way you can use conditional formatting to control the number
formatting of a cell rather than border, font, pattern etc?

What I want to do is have cells show values which are not whole numbers as
fractions rather than decimals. (It's a timesheet spreadsheet showing days
worked on projects and the cells are too narrow to show one hour as 0.125,
but 1/8 will fit nicely.)

I'm using Excel 2000.

Grateful for suggestions.