I alternate days of cardiovascular & weight lifting. I try to do 30 to 45 minutes of exercise each day & alternate between the two. So, you could go for a 30 min. walk on Monday and then lift weights for about 30 minutes on Tuesday, etc. That way, it mixes up your workouts a bit, which makes it easier to stay on track and you get the benefits of both forms of exercise. There are a lot of weight lifting books & videos & DVDs out there to help you. My favorite strength training DVD/Video is Tammy Lee Webb's "I Want That Body." It consists of six 15 minute strength workouts - 2 for buns/legs, 2 for abs & 2 for arms. You can mix them up for variety. I usually try to do one of each body part - total of 45 minutes. Good Luck!
PS - the more muscle you build, the more calories you will burn 24 hours a day!