DLookUp

Me.drwno = DLookup("lastdrwno", "tCateg2", "cat2='" & Forms!AddDrawing!ComboCat2 & "'") + 1
is same as :

SELECT
lastdrwno
FROM
tCateg2
WHERE
cat2 = Forms!AddDrawing!ComboCat2 + 1

http://msdn2.microsoft.com/en-us/library/aa172176(office.11).aspx