The default key for office 2003 professional should work. (did you checked "enabled")?
An example report to list all office 2003 keys :
SELECT TOP 100 PERCENT dbo.tblComputers.Computername, dbo.tblSerialnumber.Product, dbo.tblSerialnumber.ProductID, dbo.tblSerialnumber.ProductKey,
dbo.tblSerialnumber.Lastchanged
FROM dbo.tblComputers INNER JOIN
dbo.tblSerialnumber ON dbo.tblComputers.Computername = dbo.tblSerialnumber.Computername
GROUP BY dbo.tblComputers.Computername, dbo.tblSerialnumber.Product, dbo.tblSerialnumber.ProductID, dbo.tblSerialnumber.ProductKey,
dbo.tblSerialnumber.Lastchanged
HAVING (dbo.tblSerialnumber.Product = 'Microsoft Office Professional Edition 2003')