How Can I Select Middle .. From?

I have a table Customer with 200000 records.

When I run query

DECLARE @posTable TABLE(idkey INT IDENTITY(1,1), value VARCHAR(128))
INSERT INTO @posTable (value) SELECT CustID FROM Customer ORDER BY CustID

At the first time it takes 1 minute 42 seconds, at the second time it only takes 3 seconds.

When i run the query

SELECT IDENTITY(INT, 1, 1) AS idkey, CustID INTO #posTable FROM Customer ORDER BY CustID
The order in column idkey is not exacts


Pls. tell me why? and How can i rewrite it.