--Adapted from Aaron Bertrand's excellent SQL Resource Site: http://www.aspfaq.com/show.asp?id=2445

DECLARE 
@txtPval binary(16), 
@txtPidx INT, 
@badStr VARCHAR(500), 
@goodStr VARCHAR(500), 
@lenBadStr INT, 
@curID INT 


SET @badStr = '/ImageLibrary/GetImage.asp?liAssetID=' 
SET @goodStr = '/Assets/GetAsset.aspx?ItemID='
SET @lenBadStr = DATALENGTH(@badStr) 

DECLARE irows CURSOR 
LOCAL FORWARD_ONLY STATIC READ_ONLY FOR 
SELECT liadvertid 
FROM adverts 
WHERE PATINDEX('%'+@badstr+'%', sadvertcontent)>0 
OPEN irows 

FETCH NEXT FROM irows INTO @curID 

WHILE (@@FETCH_STATUS = 0) 
BEGIN 
  BEGIN TRANSACTION
    SELECT @txtPval = TEXTPTR(sadvertcontent) FROM adverts WHERE liadvertid=@curID 
    SELECT @txtPidx = PATINDEX('%'+@badStr+'%', sadvertcontent)-1 FROM adverts 
    WHERE liadvertid=@curID 
    UPDATETEXT adverts.sadvertcontent @txtPval @txtPidx @lenbadStr @goodStr 
  COMMIT TRANSACTION
  FETCH NEXT FROM irows INTO @curID 
END 

CLOSE irows 
DEALLOCATE irows