Passing Parameters To A Stored Procedure

Hi, I'm fairly new to TSQL so I'll try to explain as best I can.
I'm using a stored procedure to return a recordset and I'm passing a variable/parameter into it from MS Access XP, the syntax for the SQL statement is something like the following (Extremely trimmed down) :

CREATE PROCEDURE ExplodeDilutions
@MyLSN AS VarChar(8)

AS

declare tcrl cursor FAST_FORWARD for SELECT TSAMPLE.*
FROM TSample
WHERE (TSample.ISmpShortCode = @MyLsn)

The value I'm passing (@MyLSN) is 24/12359 (one LS Number)

The above statement works fine (ie returns a recordset). But what I want to be able to do is pass a series of LS numbers into the Stored Procedure. So I've opted for using the SQL 'IN' function. So the SQL statement now looks like:

CREATE PROCEDURE ExplodeDilutions
@MyLSN AS VarChar(50)

AS

declare tcrl cursor FAST_FORWARD for SELECT TSAMPLE.*
FROM TSample
WHERE (TSample.ISmpShortCode IN (@MyLsn))

The value I'm passing (@MyLSN) is '24/12359','24/12360'

This is where the problem begins because the stored procedure now doesn't return a recordset.

If I run this SQL statement thru a VIEW (manually entering the LS numbers) then the correct recordset is returned.
Also if I run the Stored Procedure using the Query Analyzer (where it will prompt me for the value of @MyLsn) and enter just one LS Number then it works fine but if I try to supply 2 LS Numbers then nothing is returned. I've tried all manner of syntax when supplying the LS numbers but alas to no avail.

So if someone could point me in the right direction then that would be much appreiciated.

Thanks in advance.