DECLARE @d1 DATETIME, @d2 DATETIME
SELECT @d1 = '1/9/2008 11:30:24.123', @d2 = '1/10/2008'

SELECT DATEDIFF(millisecond, @d1, @d2) AS Diff
/*
Diff
-----------
44975877
*/

DECLARE @d1 DATETIME, @d2 DATETIME
SELECT @d1 = '1/9/2008 11:30:24.123'

SELECT 
	DATEPART(year, @d1) AS Years,
	DATEPART(month, @d1) AS Months,
	DATEPART(day, @d1) AS Days,
	DATEPART(hour, @d1) AS Hours,
	DATEPART(minute, @d1) AS Minutes,
	DATEPART(second, @d1) AS Seconds,
	DATEPART(Millisecond, @d1) AS Milliseconds

/*
Years       Months      Days        Hours       Minutes     Seconds     Milliseconds
----------- ----------- ----------- ----------- ----------- ----------- ------------
2008        1           9           11          30          24          123
*/