Code:
	
-- Prepare sample data

DECLARE @Sample TABLE (ActHistID INT , ActivityID INT, StartTime DATETIME, EndTime DATETIME, ActivityCategoryID INT, ActivityTypeID INT)

INSERT  @Sample
SELECT  1, 163, '2007-09-24 23:00', '2007-09-24 00:00', 10006, 10022 UNION ALL
SELECT  3, 163, '2007-09-24 01:00', '2007-09-24 02:00', 10007, 10023 UNION ALL
SELECT  4, 163, '2007-09-24 02:00', '2007-09-24 03:00', 10008, 10024 UNION ALL
SELECT  5, 163, '2007-09-24 03:00', '2007-09-24 04:00', 10009, 10025

DECLARE    @Items INT

SELECT    @Items = COUNT(*)
FROM    @Sample

;WITH Yak (theOrder, theColumn, theValue)
AS (
    SELECT    ROW_NUMBER() OVER (ORDER BY CURRENT_TIMESTAMP) - 1 AS theOrder,
        p.theColumn,
        p.theValue
    FROM    (
            SELECT    CONVERT(VARCHAR(20), CONVERT(CHAR(5), StartTime, 108) + ' ' + RIGHT(CONVERT(CHAR(19), StartTime, 100), 2)) AS StartTime,
                CONVERT(VARCHAR(20), CONVERT(CHAR(5), EndTime, 108) + ' ' + RIGHT(CONVERT(CHAR(19), StartTime, 100), 2)) AS EndTime, 
                CONVERT(VARCHAR(20), ActivityCategoryID) AS ActivityCategoryID,
                CONVERT(VARCHAR(20), ActivityTypeID) AS ActivityTypeID
            FROM    @Sample
        ) y
    UNPIVOT    (
                theValue
            FOR    theColumn IN (y.StartTime, y.EndTime, y.ActivityCategoryID, y.ActivityTypeID)
        ) AS p
)

-- Show the expected output
SELECT          y1.theColumn AS Field,
                y1.theValue AS OldValue,
                y2.theValue AS NewValue
FROM            Yak AS y1
INNER JOIN      Yak AS y2 ON y2.theColumn = y1.theColumn
WHERE        y2.theOrder / @Items = y1.theOrder / @Items + 1
ORDER BY        y1.theOrder / @Items,
        y1.theOrder

SELECT        d.theColumn AS Field,
        MAX(CASE WHEN c.FromID = d.ActHistID THEN theValue END) AS OldValue,
        MAX(CASE WHEN c.ToID = d.ActHistID THEN theValue END) AS NewValue
FROM        (
            SELECT        s1.ActHistID AS FromID,
                    MIN(s2.ActHistID) AS ToID
            FROM        tSample AS s1
            INNER JOIN    tSample AS s2 ON s2.ActHistID > s1.ActHistID
            GROUP BY    s1.ActHistID
        ) AS c
INNER JOIN    (
            SELECT        ActHistID,
                    'StartTime' AS theColumn,
                    CONVERT(CHAR(5), StartTime, 108) + ' ' + RIGHT(CONVERT(CHAR(19), StartTime, 100), 2) AS theValue,
                    1 AS thePosition
            FROM        tSample

            UNION ALL

            SELECT        ActHistID,
                    'EndTime' AS theColumn,
                    CONVERT(CHAR(5), EndTime, 108) + ' ' + RIGHT(CONVERT(CHAR(19), EndTime, 100), 2) AS theValue,
                    2 AS thePosition
            FROM        tSample

            UNION ALL

            SELECT        ActHistID,
                    'ActivityCategoryID' AS theColumn,
                    CONVERT(CHAR(20), ActivityCategoryID) AS theValue,
                    3 AS thePosition
            FROM        tSample

            UNION ALL

            SELECT        ActHistID,
                    'ActivityTypeID' AS theColumn,
                    CONVERT(CHAR(20), ActivityTypeID) AS theValue,
                    4 AS thePosition
            FROM        tSample
        ) AS d ON d.ActHistID IN (c.FromID, c.ToID)
GROUP BY    c.FromID,
        d.theColumn,
        d.thePosition
ORDER BY    c.FromID,
        d.thePosition

-- Show the expected output
SELECT          SUBSTRING(p.theColumn, 2, 20) AS Field,
                MAX(CASE p.thePosition WHEN 0 THEN p.theValue END) AS OldValue,
                MAX(CASE p.thePosition WHEN 1 THEN p.theValue END) AS NewValue
FROM            (
                        SELECT          ROW_NUMBER() OVER (ORDER BY s.ActHistID) / 2 AS theSection,
                                        CONVERT(VARCHAR(20), CONVERT(CHAR(5), s.StartTime, 108) + ' ' + RIGHT(CONVERT(CHAR(19), s.StartTime, 100), 2)) AS [1StartTime],
                                        CONVERT(VARCHAR(20), CONVERT(CHAR(5), s.EndTime, 108) + ' ' + RIGHT(CONVERT(CHAR(19), s.EndTime, 100), 2)) AS [2EndTime], 
                                        CONVERT(VARCHAR(20), s.ActivityCategoryID) AS [3ActivityCategoryID],
                                        CONVERT(VARCHAR(20), s.ActivityTypeID) AS [4ActivityTypeID],
                                        d.Delta AS thePosition
                        FROM            tSample AS s
                        CROSS JOIN      (
                                                SELECT    1 AS Delta UNION ALL
                                                SELECT    0
                                        ) AS d
                ) AS y
UNPIVOT         ( 
                                theValue
                        FOR     theColumn IN (y.[1StartTime], y.[2EndTime], y.[3ActivityCategoryID], y.[4ActivityTypeID])
                ) AS p
GROUP BY        p.theSection,
                p.theColumn
HAVING          COUNT(*) > 1
ORDER BY        p.theSection,
        p.theColumn