Minimum body exercise you should do every week

I am not very particular about body exercise. I usually prefer yoga but not punctual enough. Usually the excuse for not doing exercise is not having "enough time" to do the "errand". But I am realizing now that downtime (due to bad health conditions like headache, flu, lethargy etc.) is much more than any time "saved" from not doing the exercise. So I am going to do it more frequently in 2010. (my first resolve for 2010)

Here is a New York Times links which discusses how little you must do every week.