You should ease into your running program gradually. In fact, the
beginners' program we outline here is less of a running regimen than a
walking and jogging program. The idea is to transform you from couch
potato to runner, getting you running three miles (or 5K) on a regular
basis in just two months.
It's easy to get impatient, and you may feel tempted to skip ahead in
the program, but hold yourself back. Don't try to do more, even if you
feel you can. If, on the other hand, you find the program too
strenuous, just stretch it out. Don't feel pressured to continue faster
than you're able. Repeat weeks if needed and move ahead only when you
feel you're ready.
More...from Cool Running at:
http://www.coolrunning.com/engine/2/2_3/181.shtml