Hi Steve,
To get the Customer name from AR use:
GETEXTERNALDATA("@R92ACST", "Name", "ARCUST", {Cust #})
To get the Item Description from IC use:
GETEXTERNALDATA("@N81CITM", "Description", "ICITEM", {Item #})
You don't have to type in these formulas. Just select
Edit | Insert related column or press alt-F8.