dude, if you use the word AUTOPOPULATE once more i'm gonna reach thru this machine......

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ok, the only thing you are going to do is put the DealerCodeID (which is an Autonum in the table DealerCodes) into a field in the DataEntry table called DealerCodeID (integer). On the form, we'll popluate (for viewing only) the remainder of the field from the DealerCodeID, DealerIDs and Reps tables (all joined together in a query) by referencing the columns in the combo box that the user chooses from. i know it's a little confusing, but you'll see.
using my table names and names you gave above:
Make a form with the RecordSource being the table DataEntry.
make a combo box.
Name: cboDealerCodeID
ControlSource: DealerCodeID
the ID the user chooses will be stored in the DealerCodeID field in the DataEntry table
Row Source Type: Table/Query
RowSource: SELECT DISTINCTROW DealerCodes.DealerCodeID, DealerIDs.DealerName, DealerCodes.StoreNum, DealerIDs.DealerCode, Reps.RepName, Reps.RepPhone FROM (DealerCodes INNER JOIN DealerIDs ON DealerCodes.DealerID = DealerIDs.DealerID) INNER JOIN Reps ON DealerCodes.RepID = Reps.RepID;
Column Count: 6
Column Heads: YES
Column Widths:0";1.5";0.25";0";0";0"
Bound Column:1
means that the data in the first column of the combo box (in this case the DealerCodeID) will be saved in the DataEntry table in the RowSource we specified above
ok i think that's it. you can adjust the column widths and look up other properties to adjust as you see fit.
So this will make it so a person can choose which dealership they want. from what you say, the combination of Dealer + Store Number seems to be the unique thing, so those are the two columns i made visible in the combo box when it drops down.
now, to see the other info we'll reference the columns that are in the query behind the combo box. this matches exactly how i did it when i tested it, you can fiddle around with which column has which info in it later if you want. you should just be able to get the gist of it doing this:
make a text box. label="Dealer ID".
Control Source:=[cboDealerCodeID].[Column](3)
make another text box. label = "Store Number".
Control Source:=[cboDealerCodeID].[Column](2)
make another text box. label = "Rep".
Control Source:=[cboDealerCodeID].[Column](4)
make another text box. label = "Rep Phone".
Control Source:=[cboDealerCodeID].[Column](5)
ok?
g