Transaction/Locking Question

Hi,
Very new to locking/transactions, so any help appreciated with the following:

I want to create a stored procedure with statements that read an Integer value in a single row table, return this as output from the procedure to my web form, and increment it incremented by 1 (for the next call of the procedure).

I need to be absolutely sure that while the value is being read and updated, another call to the procedure cannot read/update this value until the current is call completed, i.e some sort of locking on the value.

Question - If I wrap my SELECT and UPDATE statements in a BEGIN TRAN and COMMIT TRAN, will this be enough? e.g Is this sufficient:

CREATE PROCEDURE sp_test
@retval int output
AS

BEGIN TRAN

SELECT @retval = POID FROM OMS_SYSDATA
UPDATE OMS_SYSDATA SET POID=POID+1

COMMIT TRAN
GO

Or do I need to start using things like HOLDLOCK/UPDLOCK within statements?

Cheers
Greg