I'm trying to conditional format to highlight a date cell if its in the
current week.

I know whow to use WEEKNUM to check a week's number (1-53). I did check to
make sure the Analyst Pack was loaded.

The challenge I have is getting conditional formatting using formulas to
check the current cell

I'm trying the following formula: (In Conditional Formatting)
="WEEKNUM($C$4,1) = WEEKNUM($A$1,1)" with no results
C4 is the current cell, A1 is a refernce cell with TODAY().