Trigger To Seperate Alpha From Numeric

We have a table with an indesx that is varchar(7). It contains up to 5 numbers and 2 characters to denote batches. IE. 100a
105zz
1c
2
10001w

In an Access gui I need to be able to sort this field numericaly so each number shows up in its correct position. IE.
1c
2
100a
105zz
10001w

In order to accomplish this, I created a seperate field on the table named Num as varchar(5). I would like to create a trigger that updates this field any time a new batch number is entered. This way I can have my queries order by Num when returning the recordsets to the GUI.

Below is the code that I thought would work, but it is giving me an error near the keyword BEGIN after the IF(ISNUMERIC) statement. I can't seem to find an error with this code, but I thought maybe a thousand fresh sets of eyes could. Any help would be greatly appreciated. Also if you know of a better way to accomplish this task, please feel free to post here.

TIA,

Aaron

CREATE TRIGGER [InsertNum] ON [dbo].[IP_Batch_Table_Temp]
FOR INSERT, UPDATE
AS

DECLARE @Num varchar(7)
DECLARE @Num1 CHAR(7)
DECLARE @x INT

SET @Num = (SELECT IP_Batch_Number FROM inserted)
SET @x = 1
WHILE (@x < len(@Num))
BEGIN
IF (ISNUMERIC( SUBSTRING(@Num, @x, 1) ) )
BEGIN
SET @Num1 = @Num1 + SUBSTRING(@Num, @x, 1)
END
SET @x = @x + 1
END
UPDATE IP_BATCH_TABLE_TEMP SET NUMBER = ltrim(rtrim(@Num1)) WHERE IP_BATCH_NUMBER = @Num