I want to use data validation and conditional formatting together, so that...

1) the user is limited to entering a number = 0
2) if the value is 0 the cell is red
3) if the value is 0 the cell is green
4) if the value is nothing (blank) the cell stays the same.

I'm using Excel 2000, and can't seem to get the combination of these 2
things to give me the results I want. Any ideas?

Thanks.