How about this one :
ALTER PROCEDURE [dbo].[InsertOrder]
@CustomerID varchar(50),
@OrderDate datetime,
@FirstName varchar(50),
@LastName varchar(50),
@Company varchar(50),
@Address varchar(50),
@Country varchar(50),
@City varchar(50),
@Province varchar(50),
@ZipCode varchar(50),
@Telephone varchar(50),
@Fax varchar(50),
@totalAmount varchar(50)
AS
BEGIN
declare @uid int
select @uid = userid from users where CustomerID=@CustomerID
INSERT INTO ORDERS(CUSTOMERID,ORDERDATE,FirstName,LastName,Company,Address,Country,City,Province,ZipCode,Telephone,Fax,totalAmount,userid)
VALUES (@CustomerID,@OrderDate,@FirstName,@LastName,@Company,@Address,@Country,@City,@Province,@ZipCode,@Telephone,@Fax,@totalAmount, @uid)
SELECT @@IDENTITY
END