My First Complex SP - Feedback Please

hi. ive just written my first complex SP for SQLServer 2005. id be REALLY grateful for any feedback please. if there's anything i'm doing wrong then it's better that i know sooner rather than later! im wondering if its over complex or just plain wrong. please bear in mind that i have at least made an attempt at this, this is my first proper SP.

the SP that I have written is to insert an Account and a User. The SP should do the following.

1. Start a transaction.
2. Insert a user by calling a nested SP. if the return value is greater than zero then the user has been successfully inserted.
3. only attempt to insert an account afterwards if the user has been inserted successfully.
4. if the user or account insert is not successful then rollback. otherwise commit the transaction
5. return an error code from the SP as such: 0 = success. 1 = failure, a user already exists with the given username. 2 = an unknown error occurred whilst inserting the user. 3 = an unknown error occurred when inserting the Account.

here is my code:

CREATE PROCEDURE sp_Account_I
@Id_Package smallint,
@Amount money,
@Username varchar(16),
@Password varchar(88),
@FirstName varchar(32),
@Surname varchar(32),
@DateBirth datetime,
@Email varchar(64),
@Id_Country int,
@Id_Account int OUTPUT,
@Id_User int OUTPUT

AS

DECLARE @ErrorCode int;

BEGIN

SET NOCOUNT ON;

SELECT @Id_Account = -1;

BEGIN TRANSACTION

/* Insert the user. */
EXEC @ErrorCode = sp_User_I1
@Username,
@Password,
@FirstName,
@Surname,
@DateBirth,
@Email,
@Id_Country,
@Id_User OUTPUT

IF @ErrorCode > 0
BEGIN TRY
INSERT INTO Accounts(
Id_Package,
Id_UserMain,
Amount)
VALUES(
@Id_Package,
@Id_User,
@Amount)

SELECT @Id_Account = SCOPE_IDENTITY();

END TRY
BEGIN CATCH
SELECT @ErrorCode = 3; /* An unknown error occurred. */
END CATCH;

IF @ErrorCode = 0
COMMIT TRANSACTION
ELSE
BEGIN
ROLLBACK TRANSACTION
RETURN @ErrorCode;
END

END