Icon set based on another cell

[NeoFax]

I have a row of information that I would like to check if they meet
certain criteria and then place a icon in the cell using conditional
formatting. Currently my data is like thus:

Material A Planned 1 jan 10 12 jan 10 26 jan 10
Shipped 12 Dec 09 17 Dec 09 23 Dec 09

What I would like to do is have a green icon if shipped is less than
planned - 30, yellow icon if shipped is between planned - 30 and
planned, red icon if >= planned.

 

[Andy Smith]

It's easiest to use conditional formatting to simply color certain cells red,
yellow or green. I don't think displaying on of three graphics is possible.