Hi Jim
Use the WEEKNUM function, e.g:
=WEEKNUM(A1)
Where A1 houses the date.
I think this might have been part of the analysis toolpak in version 2003, so if you are using that version (or earlier), make sure you install that addin (Tools > Addins).
Also, if using TODAY(), best would be to house it in a name:
Name: Today
Refers To: =TODAY()