Excel 2003 Conditional Formatting - Student Targets

Ive been asked to look at conditional formatting forthe student target grades excel sheets. The formatted cells will be compared to his target grade cell, if hes doing better it will be green, on target orange, and worse red.

The grades are structured as such;

Highest

...

5a

5b

5c

4a

4b

4c

3a

3b

3c

...

Lowest

As you can see the number works as usual; 5 is greater than 4. But the letters work the other way round; a is greater than b.

Because of the letters bit Im a little stumped in how to do this. Any ideas?

Cheers