Assigning multiple values to a parameter in stored procedure

Hi:
How do you write a SQL statement in a stored procedure so
that it will allow you to assign multiple values to a
parameter?
For instance in this example below, depending on what the
users select on the front-end application, the values
assign can be one customer id value or multiple customer
id values:
Create procedure dbo.SP_Test
As @.CustID varchar(3)
Select * from tblCust where customerid = @.CustID
Please help!This is probably not the best solution but it should work
create procedure sp_test
@.cust_id varchar(50)
as
set nocount on
exec ('select * from tblcust where customerid in (' + @.cust_id +')')
go
This procedure would be called as sp_test '50' for one cust_id or sp_test
'50, 55, 100' for several cust_id's