I'm faced with a problem a little over my head... again :-)

I need to exclude certain entries from the calculation of an inventory report. The problem is the perameters for the entries I need to exclude from the calculation are in a different file than the actual inventory information. The two files do have a common field name to reference to each other, but I'm not sure how to make the program look at each of the files for the comparison.

To diagram it I'll call the inventory file FILE1, the other data file FILE2, the field which I can use to reference the two files COMMON, and the data I need to exclude BADDATA:

FILE1 is what all the computations are figured from, and contains COMMON. FILE2 contains COMMON and BADDATA. I only want to exclude entries that have a value of W or X in BADDATA.

I've got absolutely NO idea how to go about this... help?