Refer to KB79539 - "How to determine what tables are in a Crystal Report work file" on the Sage 100 Knowledgebase.

ok got it. Thank you. How do i know what fields are used in each table?

That report is a bit of a special case... the usual UDF trick doesn't work, and even if it did the summary table's (IM_PeriodPostingHistory) raw data is not stored in an Excel friendly format (because the beginning amounts are only stored for period 1, and the programming does calculations for 2-12 as the work table data is being generated).

If you want an Excel / pivot table friendly strategy, the true raw data is in the IM_ItemTransactionHistory file (unfiltered, from the beginning of time... which can be a huge data set).  With Premium you can do a SQL view which does a lot of that data crunching for you (with SQL server being much better at handling large data sets, compared with Excel).

I have pulled in the IM_ItemTransactionHistory data to excel. I can see that when i add the IM_InventoryValuationbyPeriodWrk file that has the quantity & value at period end that it breaks my data pull. the end goal here is to create a report that will allow me to pull inventory levels on a weekly basis and track over time. 

The work table is always blank and cannot be used for anything like an Excel query or custom report.  The idea is to use the TransactionHistory table to re-create the by-period values manually.

ok i got that, but how do i group transactions such that I can set the period i want to report inventory balances? i.e. if i want see inventory levels every Monday morning

I personally wouldn't use Excel... I'd do this type of reporting with Crystal Reports or directly in SQL.  Perhaps someone else has some tips to get you the rest of the way there.  My guess is SUMIF...