Pivot Table & Monthly Worksheets

I want to create a summary pivot table report + chart. What I have is 12 worksheets, one for each month, each with total amount invoiced and gross profit by client.

I want a pivot table that shows me the clients and amounts each month (this is the bit stumping me). Basically I want a drop down box to select the month on the pivot table, which then shows the data from the relevant worksheet (Aug-09, Sep-09 or whatever).

I've tried using multiple consolidation ranges but this just aggregates all the data; it doesn't allow me to limit by the worksheet the data has come from.

I'm wondering if I have to consolidate all my months into one big sheet, then add a field for the month. I would rather avoid this but accept it might be the only way.

Final thing; can't use VBA at all (too much hassle for IT apparently).