I've got Harry Potter 1-4 on my shelf next to the rest of my Japanese learning books. It's quite a task to read them, but every once and a while I'll sit down, pull out a paragraph and copy it down into my note book. Then I'll look up every word I don't know and make a list.
I wish I could tell you that you could probably read them by the end of the year if you have enough gumption, but it's probably only a little easier than reading a Japanese newspaper, in my estimation.
Considering that kids in Japan start learning Kanji in 1st grade, there isn't a whole lot of material out there that doesn't require it. I would suggest
the Mangajin books if you're looking read real Japanese with a great deal of help. After a few (okay, a lot) months, you should then move onto books such as
Breaking into Japanese Literature, but there's just no getting around the fact that "several years" is probably a realistic, or even a little optimistic, estimation of how long it will take you to get to that level.