Calculating sums for a found set in a related table

I'm trying to create a report to compare inventory levels from one month to the next. I have a table where all the inventoried items are received and created (including the initial quantity) and another table where all the transactions (deductions, additions) are stored. The balance remaining for each item is calculated by taking the initial quantity from one table and adding/subtracting the amounts from the different transactions in the other table. Is there any way that I can 'hide' certain transactions (based on date of transaction) to be able to go back and recreate an inventory snapshot on a particular day. For instance, 'hiding' the July transactions to give a snapshot of the inventory at the end of June.

I then need to create a report that will show the June snapshot versus the July snapshot (at the end of July). Is there any easy way that anyone can thing of to be able to do this?

Any help would be appreciated...I'm stumped!

Thanks!