Group dates into weeks

You can do this with formulae, see the attached workbook.

By putting this in say A1

Formula:

=TODAY()

In A2, this assumes that your input list always starts with a Monday

Formula:

=Input!A3

Then in A3, drag/Fill down

Formula:

=IF(COUNTIF($B$2:B2,"")>5,"",IF(A2<=$A$1-7,A2+7,A2+1))

See the workbook for the formulae in B2:D2

This will work dynamically, drag A20:D20 down to extend the table as your input data grows.

Note that Sheet "input" ColumnB "Day" isn't required.

Also your profile states you are using 2003, but the sample you attached is 2007 or above.
This will not work in 2003, although it can easily be adapted if required.