" that is very beneficial. Here is an article that specifies certain poses and stretches you can do, and how to do them: http://www.cbsnews.com/stories/2010/01/21/earlyshow/health/main6123419.shtml
Doing the desk yoga will also help alleviate lower back pain that is associated with sitting for long periods of time.
If you prefer to save any exercise for when you get home, I would suggest starting with a core workout or yoga. Beginning Pilates is a great way to build up your core and stabilization which will also help with back pain. Here are some great videos you can get to help you out: Element: Pilates Weight Loss for Beginners, Pilates For Beginners (3 DVD Set), Yoga For Beginners, Yoga For Beginners (3 DVD Box Set)
I started with Pilates For Beginners (3 DVD Set) nearly a year ago (before I became a couch potato). It's a fun way to get off the couch and away from the computer and start becoming healthy.
Tip of the day - Get off your butt! Periodic activity throughout the day will reduce your risk of heart and health problems. Take 5-10 minute breaks several times a day and stretch or walk to get your blood flowing and skip the coffee :)