[Excel 2007] Conditional Formating

I am trying to get my spread sheet to turn some different collors.

If Z2=A then turn the row red
If Z2=B then turn the row green.

I have tried a few things, but i can only get one or the other

VBA?

a = 1
b = 2

If Worksheets("sheet1").Cells(1, 1) = a Then
Worksheets("sheet1").Cells(1, 1).Interior.Color = RGB(200, 100, 100)
Else
If Worksheets("sheet1").Cells(1, 1) = b Then
Worksheets("sheet1").Cells(1, 1).Interior.Color = RGB(100, 200, 100)
End If
End If