Writing to another workbook

[Eric Hearn]

Using Excel 2003.

I have a workbook for generating invoices (WB1) which contains fields for
Delivery Note No. and Invoice No. and another workbook (WB2) with 2 columns
using these fieldnames as column headers, with the Delivery Note No. column
being pre-populated with an appropriate series of numbers.

I want a routine that will look up the Delivery Note No. on WB1 in WB2 and
write the Invoice No. alongside it.

Any help greatly appreciated.