One of the first hurdles involved in getting in shape is establishing goals and setting up a rigid and strict diet/exercise routine. I don't care what anyone else tells you - if you want to lose weight or make gains of any kind you have to sacrifice in order to get there. In general, the more you sacrifice the larger your weight loss/gains.
Walking is an excellent form of exercise and probably your best bet considering your current weight. One mile every other day is not nearly enough to get yourself in shape or lose any amount of significant weight. I would suggest at least 3 miles/day for 5 days of the week. If you think that's too much and that makes you apathetic, then try less, but you're not going to lose 70lbs any time soon through a lesser routine. Up the distance or the speed at which you walk the 3 miles every week by about 5-10%. Never increase both at the same time because you risk injuring yourself and setting yourself back. I would HIGHLY suggest adding a weight lifting routine as well. You don't need to have some hardcore workout plan, but basic exercises like bench, squats, curls, tricep extensions, and military press would help build and tone (the more muscle you have, the more calories you burn, and so the more weight you should lose). However, do not substitute weight lifting for cardiovascular exercise - your goal is to lose weight and so you MUST focus on cardiovascular activity. I would suggest trying to do as much extra activity as you can (park you car far away from stores, always take the stairs, do as much outdoor activity as you can, in addition to the walking routine).
Your diet will dictate whether you lose weight or not. The formula is simple...if you intake more than you burn, you will gain weight. However, if you intake less than you burn you will lose weight. Cut back on your eating portions in a BIG way. I'd suggest eating about half as much as you normally do. Do NOT drink soda of any kind (or any beverage with tons of sugar - i.e. iced tea, lemonade, juices of different sorts). If you're head is really in the game, I'd advise only drinking water. Drink lots of water as often as possible. Also, whenever you need a snack (which should be every 2 hours or so) make sure to eat a piece of fruit instead of snacks of some kind like chips, cookies, doughnuts, or other high calorie, high fat alternatives. Stay away from the likes of pizza and oily foods and try and eat simply. Rice, fish, and a side of vegetables is excellent (substitute fish with chicken or even beef if you like, but remember to stick with SMALL portions). A daily sampling of your diet should look something like this:
cereal with nonfat milk
piece of fruit and some nonfat cottage cheese
lean turkey sandwich with baked lays potato chips (sandwich should be simple: turkey, lettuce, tomato, multigrain bread - no mayonaise or other spreads)
piece of fruit
nonfat cottage cheese
salmon, rice, vegetables (small portions and do NOT eat late at night)
Good luck.