Return Array Index Number For Specific Date

I looking for a macro which will help to open a file with current week number in name.

The problem is week 1 is starting on 30/03/2008 (finacial year) and ends on 28/03/2009.

I've made two dimensional array (week number, weekday) with all the dates from that period.

I have problem with code to search through the array for given key, return index and write it into variables.

For now my code looks like:

Sub week()

Dim i As Long
Dim j As Long
Dim k As Long

Dim week(51, 6) As String