Conditional Formating can do this.
In Excel 2003, select the cell in row 6,
Format,
Conditional Formating,
Formula is,
Replace A$6 with whichever cell contains the date.
If your target date can change, and you want to control it by storing it in another cell, replace date(2011,6,20) with the reference for that cell.
Apply a format as required.
Then copy, select the entire column, paste special, formats.
In later versions of Excel I think the menu paths may be slightly different, but the general principle will still apply.