[Forms]![form1]![champ1]
refers to a Microsoft Access form called form1 which has a control on called champ1
you could try saving the following stored procedure to work in a similar manner
CREATE PROCEDURE [sp_YourProcedure]
@champ1 varchar(255)='%'
as
SELECT champ2 FROM Table2
WHERE champ1 like @champ1
Then by executing the stored procedure you, by default, get all records. If you then supply a parameter then you only get the values corresponding to the value supplied
Hope this helps
Andy