I'm sure there must be a simple way of doing this ...

I have a worksheet where the column headers (ie; cells A1:L1) are dates -
the first of each month going back for 12 months. So, A1 is 1 Nov 2007, B1
is 1 Oct 2007, etc.

What I need is for cells B1:L1 to update automatically when I change the
value of A1 to the first of the current month. So, when A1 becomes 1 Dec
2007, I need B1 to become 1 Nov 2007, etc.

The only way I can think of doing this is by using EOMONTH. Hence, B1 =
EOMONTH(A1,-2)+1. This works OK but to use this function I had to load one
of the add-ins (Analysis Toolpak?) and I notice that when the spreadsheet is
e-mailed to users who have not loaded this, the NAME error is shown until it
is loaded. As the recipients are a large group with mixed IT abilities, I
can forsee problems asking them to do this!

There must be another way?!

Thanks.