Jenny,
Hey I'm the same height as you and near the same age I think. I just really really REALLY want to caution you on setting your "goal" at 100 lbs. Right now you are a smidge over "healthy" weight (by 2 lbs or so). It sounds like your goals are more on toning your thighs and tightening your stomach. Let me tell you my story (I'll try to be short) and perhaps that will help you understand the warning.
I gained a bunch of weight in college, I think I got up to 160 lbs. I was fit, but quite heavy. I like to be active and it was slowing me down so I decided to lose weight. I set my goal at just under 100 lbs. It sounded so perfect and dainty and petite. I tried a few diets but I ended up with essentially an eating disorder. I would drink juice, milk, smoothies, and soups and would try to throw up if I ate "real food" because I usually ended up overeating or feeling like I did. I also exercised for at least 3 hours every day. Yikes! This got to its worst point when I was student teaching. I can't say it was "oh I want to be thin" it was more a control point. And when you start losing weight it gets addictive. I got down to 102 pounds, but my hair got thin, my skin was dry, I was freezing cold all the time, I felt jittery but tired, and I stopped menstruating. Even though it was "technically" still a healthy weight, it wasn't.
Now you might never be so stupid but I did want to give you that caution. Now I'm back up around 128, get my period, and am healthy, but who knows what I messed up in my body by doing that! My doctor says that 120 to 130 is a very healthy weight for me and below that is not, in part, because I am fit.
I know all the program experts and calorie counters are going to jump me for this one, but I don't recommend doing all that. Look at the pyramid guide. You need whole grains, lots of fruits and veggies, lean proteins, dairy, and healthy fats. Just try to keep that in mind as you make eating decisions. More importantly listen to your body. Eat breakfast. Wait until you are hungry to eat. Eat until you are satisfied (satisfied not full!). Don't eat until you are hungry again. Splurging is great! But don't do it until you are hungry and wait to eat again until you are hungry again. Hungry being that grumble in your stomach, not just boredom or emotions. Water is good. Walking is great exercise. Keep making sure that you walk with energy (don't dawdle). Join a gym or get some weights or grab some food cans. Try to strength train for 20-30 min 3-4 days a week. Do sit ups and things that make you feel your thigh muscles (leg lifts, squats, etc) hurt a bit.
Remember the faster you lose it the more likely you are to gain it back. Make little changes and you are more likely to stick with them. If you lose one pound every month, that's twelve pounds in a year.
Some people need to make a production of weight lose for it to happen. For me, that just messes me up. Instead I just consider the decision I'm making when it comes and deal with the present.
Then again running doesn't hurt either!
ps. I like your sig quote!