I think I'm the one who recommended C25K to you. It worked wonders for me! These days, you've seen how I once did a half-marathon and ran the whole thing despite severe injuries, and under more normal circumstances, I run a little less than three miles (three laps around my apartment complex' outer track, which is calculated to be something like 0.9 miles per lap) as just part of my normal exercise routine, three times a week. This was all after several false starts around my college years, wherein I was an idiot who didn't really understand the whole "if you go from zero to killing yourself on the very first workout, you're just going to injure yourself within a week and then stop again." C25K is what finally brought me to this level!

Unfortunately, I have a bit less to say on the subject of motivation; clearly mine is fine, but that's because I have the prurient ulterior motivation that maintaining a lithe Final Fantasy villain frame just happens to appeal to me, as does the fact that hitting that rough dirt-with-rocks track barefoot regularly toughens my feet at the same time it does all the regular calorie burning and fitness enhancing and whatnot. Obviously, this kind of motivation works great for me (the latter especially,) though I can't exactly think of a way to make it relevant to you ... so, yes, level-based structure progression, let's go with that. :)