Activating a workbook that was previously active

Here's the problem... An Excel file is e-mailed to my company for all the credit card transactions in a given day. Because we manage many stores and each store is a different legal entity and a different fiscal year ending, I need my macro to sort the information and separate the transaction by store and by fiscal year end. I just hit my first block. I need to open a workbook off the server to grab information for a vlookup formula. I can get the workbook open, but I can't get back to the original workbook or find a way to reactivate it. Because the macro is going to be saved in the "personal" workbook, I can't use the "thisworkbook.activate" code. Also the workbook name and tab name that is emailed to me will always be different so I can't use other solutions that I've seen posted. Any Ideas?

You don't actually need to activate workbooks with VBA, also please wrap your code with Code tags