First off, I'm right there with you on the crazy dog lady thing. Sort of... I have 2 dogs myself and have tried -keyword being tried- to get a third for a few months now. Three different dogs have come in and out of my house before I've finally called it quits. I don't know what the big difference is between 2 and 3, but for some reason it's just too many for me! If I could, I would have some land a ton of dogs roaming it. Hah! I love dogs.
It's kind of funny because I myself am completely motivated to lose my weight and get into shape so that I can enlist. I've never really had a goal like that and because of that goal, I have the most motivation to lose weight I've ever had in my life. Also the greatest fear of failing because I'm inching closer to the age cut off for the Air Force.
I think like Candeka said, you should definitely look into a fitness video or just getting out and walking! Not sure where you are and what the weather is there, but I know it's still chilly here, so for starting out, the fitness video might be the way to go. I'm looking into getting Jullian Michaels' 30 Day Shred (lots of forum threads on that) and Walmart sells it online for $7 and according to the website -I'm going to go check the store today- they have a kit that includes the DVD, a mat and 3lb weights for $20. So it's relatively inexpensive. Forgo the pepsi 24 pack and buy a DVD instead? I know that's asking a lot to go cold turkey. Instead though, have you tried the Pepsi One or Diet Pepsi (I think that's what they're called? I'm a Coke fan personally). Another thing I'll suggest with the diet colas is that for me, the Cherry Coke Zero tastes amazing. I think the cherry flavor gives the "diet" soda a little more kick. Maybe kind of try to wean yourself? I used to have at least 1 can of Cherry Coke Zero a day and sometimes 2, but since I've been more conscientious about my water intake and just what I'm eating period, I haven't touched a soda since I started almost a month ago.
Another thing I'll add is to make sure that you're eating enough, especially if you start some moderate to heavy intensity exercising. I struggled with this myself and my mother is driving me crazy because she's barely eating...and eating all the wrong things! She thinks it's ok to have one or two meals a day that total 600-700 calories. You need to find some healthy meals and snacks that will keep you satisfied instead of running to the store for the junk food. Keep a bag of baby carrots in the fridge and some fruit and tell yourself that if you're hungry (or even if you just want to put something in your mouth) that, that's it. You get that or nothing. I personally never was a big veggie eater, but since I've started bringing them in the house, I have turned to them or sometimes even just turned around and didn't eat anything.
In any case, I wish you the best of luck! You can totally do it!