Don't let the ADD put you off, I also have ADD but I'm managing to put GTD into place without any real problems. Even though I'm not totally up and running yet, I've found that it's already made a huge difference to my level of organisation and I feel much more in control and on top of things.
I'm still sorting through the piles of stuff in my in-box but doing the mind sweep was really helpful. Being given permission to put stuff on a someday/maybe list was particularly useful to me.
Do get a labeller, it's the thing that I've enjoyed the most while implementing the system and enjoyment is often key for ADD people. I still can't believe how much easier it is to read my files now. I bought a whole load of manilla files and a bigger filing cabinet and filing is a pleasure now. I'm slowly getting every relevant piece of paper in there.
Also, expect it to take a bit of time, mine is taking weeks rather than days. Doing it in small bite sized chunks helps.