Name File Based On Date & Week Number

on a macro i use to open, update a file and then save it in an archive.

Opening and updating the file is no problem, but i want to save under a dynamic name in a folder structure. This is a reoccurring task, and this way I update the same file each period but save a copy with the current data in an archive under a different name in the right place of a directory (archive).

My idea is to have a hidden cell in this workbook, where I can have the name calculated by simpe excel-formula, i.e. ="Filename_"&WEEK(TODAY())&"_"&YEAR(TODAY())&".xls".

The file should go automatically into an archive-directory, lets say C:data....archive2007 (2008, 2009, etc)
I want to add the last folder to my filename, so my macro knows the first part of the path and has to go look up the actual name it gets in order to be saved.

So I end up with a cell containting the filename: 2007Filename_35_2007.xls

Now I only need the macro which looks up this name, adds it to the hard programmed path:
C:data...archive
so that the file gets saved under as: C:data....archive2007Filename_35_2007.xls

this is how i start:

Workbooks.Open Filename:= _
"C:data....Filename.xls"
' here the file is updated...
Windows("Filename.xls").Activate
ActiveWorkbook.SaveAs Filename:= _
"C:data....archive'(how do i do this?)'", _
FileFormat:=xlNormal, Password:="", WriteResPassword:="", _
ReadOnlyRecommended:=False, CreateBackup:=False
ActiveWorkbook.Close