got an immediate solution w/o any fix. use the equation to subtract field one and two ->

<%
Set X=Server.CreateObject("ASP.db")
X.dbUnit=2002
'X.dbDSN="provider=Microsoft.Jet.OLEDB.3.51; data source=c:\uno\dev\nwind\nwind.mdb"
x.dbdat="localhost,northwind,sa,sa"
X.dbDBType="SQL"
X.dbMode="Grid"
X.dbGridinc=10
X.dbSQL="select ProductName,UnitsInStock,UnitsOnOrder from Products"
X.dbGridTableTag="BORDER=2 Cellspacing=2"
X.dbMagicCell = "1,,(<<#1#-#2#>>|GTN|0|BGCOLOR=green|#1#~|EL||BGCOLOR=Red)"
X.ASPdb
%>