Yoga may just be the perfect cross training for running as it builds endurance and flexibility. It should help you avoid injuries. Also, if you are trying to lose weight, the yoga is going to really help as the running in the C25K does not burn as many calories (especially in the beginning) as you likely need for real weight loss. Best of Luck!
That is an excellent idea! Yoga is perfect for runners because it helps improve flexibility, which can be a problem for runners who don't spend extra time on flexibility. This will help prevent injury, which is a good thing, but yoga has so many great benefits on it's own! I practice Kundalini yoga and every now and then throw in a hot yoga session, and I find it extremely refreshing and a great way to improve the body for running. Definitely do it. It will definitely be a good decision!