Excel 2007 : Pivot Tables with different groupings based on same data table

In Excel 2007 I have one data table, say Dates by $Sales, and want to create and save two pivot tables & their charts, one grouped to give Sales by Weeks, the other, Sales by Months. If I create the weekly tabe, then try to create the monthly table, the weekly table changes to monthly.
I could create two separate data tables, one per worksheet, and create the pivot tables & graphs on each sheet, but then I'd give up the ability to add new data to only a single master table. How can I keep the groupings in the 2 pivot tables distinct without losing the ability to update each of them when the master data table is updated?

Thanks for any tips.

Just create a copy of the first sheet and change the grouping in the copied table. Both tables will refresh at the same time.

Alternatively, crreate a pivot table from scratch as you normally would. In the first couple of creation steps you'll have the option to base the new table on an existing table or create a brand new one. Baseing on an existing table will also allow for two pivot table with distinct groupings that refresh simualtaneously.