Hey trustycat. I wouldnt worry too much about not being able to run massive amounts. Walking is just as benefitul as running. I've just always enjoyed running, so thats really why I decide to do it. Plus running can be hard on your joints etc. and thats why its so important to stretch. (like I sometimes dont do! =)
But just enjoy yourself and do as much as you can. My fiance is in the Air Force and he's a big runner like myself, yet he's in the military so ya know how they are about ,PUSHING TO THE EXTREME! =) He's always telling me/himself how its so good to push, push, push yourself as hard as you can! I know how to improve etc. you've got to "up" your workouts etc. but this only causes me to feel stressed and I dont enjoy my run. What I've done lately is to run at a nice pace, nothing extreme, just a pace that feels good. I'm sure over time I'll improve gradually, but I'm not all freaked out over my run "times". So girl, dont stress yourself out about what you feel comfortable doing. Everyones different. And the more you do your walking, the better you'll get and you'll be able to walk faster/longer etc. without getting out of breath. And to answer your question, as far as carbs go...What I do is make sure I've had some broccoli or something substantial an hour or so before I go to the gym. Maybe its in my "head" or maybe it really does work, but I havent really felt any different running now than when I did running a while back after eating a bowl of pasta! So just keep it up and your doing fine! =)