Using The IN Keyword With A Parameter In A Stored Procedure

Here is the beginning of a stored procedure that I am trying to use as the source of data for a Reporting Services report.




Code Snippet
CREATE PROCEDURE udsp_mrkt_anal
@source varchar(8000),
@weeks int


AS

DECLARE @campaigns table (glcid int, campdate datetime)
DECLARE @entitycamp table (enid int, glcid int)
DECLARE @campcount table (glcid int, opps decimal (18,0), revenue money)
DECLARE @camps table (opid int, begdate datetime)

INSERT into @campaigns

SELECT glcid, [date]
FROM gl_campaigns
WHERE source IN (@source)






So, what I am trying to do is allow users to pick multiple source ids to be returned in the report. However, SQL doesn't see them as that in the stored procedure and I am assuming is just converting them to a string for example: '1, 2, 3, 4'

My question is, how can I make this work with a stored procedure and having the user pass multiple ids through, in this case, a report parameter? The same solution would probably work for just executing the sp straigt out as well.