calculate number of hours between two date/time combinations

[smokebreak]

Hello,
I am trying to find a way to calculate the number of hours between date/times found in separate rows. The attached data set will help to envision what I am talking about.

For each couple of rows, I need to find a way to calculate the number of hours elapsed from row 1 to row 2. In the first example, to calculate the number of hours between 12/2/2009 8:56:51 and 12/4/2009 6:35:27.

any help is appreciated!

Thank you