How do I or can I put a vlookup or hlookup in conditional formatti
 

I am trying to work with dates by changing the colours of the cells depending
on a date in one cell being compared to a date in another cell. This works
fine. However, I now want to turn another cell another colour depending on
the date in the formatted cell above and data in a second cell based on a
list (eg below). Hope this makes sense. Eg..

Date Reply
04/05/2005 Planned
05/05/2005 Unplanned
06/05/2005 [blank]
07/05/2005 Planned

.....etc
In a worksheet it would usually be =vlookup(a1,range,2,false) but can you do
this in conditional formats and if so what is the formula format?