Filtering Results In The Where Clause Vs A Having Clause

I am working with a vendor on upgrading their application from SQL2K to SQL2K5 and am running into the following.

When on SQL Server 2000 the following statement ran without issue:

UPDATE dbo.Track_ID

SET dbo.Track_ID.Processed = 4 --Regular 1 leg call thats been completed

WHERE Processed = 0 AND LegNum = 1

AND TrackID IN

(


SELECT TrackID

FROM dbo.Track_ID

GROUP BY TrackID

HAVING MAX(LegNum) = 1 AND


TrackID + 'x1' IN


(


SELECT

dbo.Track_ID.TrackID + 'x' + CONVERT(NVARCHAR(2), COUNT(dbo.Track_ID.TrackID))

FROM dbo.Track_ID INNER JOIN dbo.transactions


ON dbo.Track_ID.SM_ID = dbo.transactions.sm_session_id

GROUP BY dbo.Track_ID.TrackID

)

)
Once moved to SQL Server 2005 the statement would not return and showed SOS_SCHEDULER_YIELD to be the waittype when executed. This machine is SP1 and needs to be upgraded to SP2, something that is not going to happen near time.

I changed the SQL to the following, SQL Server now runs it in under a second, but now the app is not functioning correctly. Are the above and the following semantically the same?


UPDATE dbo.Track_ID

SET dbo.Track_ID.Processed = 4 --Regular 1 leg call thats been completed

WHERE Processed = 0 AND LegNum = 1

AND TrackID IN
(



SELECT TrackID

FROM dbo.Track_ID

WHERE TrackID + 'x1' IN


(


SELECT dbo.Track_ID.TrackID + 'x' + CONVERT(NVARCHAR(2), COUNT(dbo.Track_ID.TrackID))

FROM dbo.Track_ID INNER JOIN dbo.transactions


ON dbo.Track_ID.SM_ID = dbo.transactions.sm_session_id

GROUP BY dbo.Track_ID.TrackID

)
GROUP BY TrackID

HAVING MAX(LegNum) = 1

)