According to Livestrong.com you CAN get in shape for a 5K in just a few weeks. Granted, some prior experience running is required. If you're ready to race for the cure and need a little guidance head over to the Livestrong website or follow these brief details.
1. Train gradually. It is important to build up a level of cardiovascular endurance as well as muscular strength and endurance in order to allow your body to adapt safely. If you're a beginner this could take eight to ten weeks. Trying to train in a shorter period may not be enough time to strengthen your legs and your lungs, although if you already have a good level of fitness from other sports like swimming and running, you may be able to do so in two to four weeks.
2. Build a base. When first starting, you should be able to walk at a brisk pace, 15 minutes her mile, for 30 minutes. If you can't, build your walking distance first. Then add running. ACE Fitness recommends running 2 minutes, then walking 4 minutes. Repeat the cycle for 30 minutes and progress each week by reducing how long you walk.
3. Vary your training. Champion runner and coach Hal Higdon says vary your training through the week especially if you're new. He advises three days of running and one or two days of walking. Gradually increasing your running distance is also a good way to train.