<%
set conn = Server.CreateObject("ADODB.Recordset")
set rs = Server.CreateObject("ADODB.Recordset")
conn.open MM_Collaudi_STRING
rs.open "SELECT * FROM TARGHE WHERE TARGA='" + Replace(comandotest__varsigla, "'", "''") + "'&'" + Replace(comandotest__varnumero, "'", "''") + "'", conn
If rs.eof Then
set comandotest = Server.CreateObject("ADODB.Command")
comandotest.ActiveConnection = MM_Collaudi_STRING
comandotest.CommandText = "INSERT INTO targhe (targa) VALUES ('" + Replace(comandotest__varsigla, "'", "''") + "'&'" + Replace(comandotest__varnumero, "'", "''") + "') "
comandotest.CommandType = 1
comandotest.CommandTimeout = 0
comandotest.Prepared = true
comandotest.Execute()
else
' la targa esiste già
end if
rs.Close
conn.Close
set rs = nothing
set conn = nothing
%>

almeno credo...

PS: le stored procedures sono un'altra cosa.