We have the same problem with our 12 year-old-son. We recently got a six-week interim report and he was going to fail some of his classes because he forgot to turn in assignments--most of them he had already done! He is a very smart boy and has been able to skate by with minimal effort until this year (7th grade). He was very resistant to medication for ADD until this last report card.
One thing that has helped somewhat is that my husband goes through my son's day with him at night. He asks him about what he did in each class, what is coming up, etc. My son is supposed to write it all down in a planner, which has been a learning process. Recently we added the requirement that he also has to call the homework hotline to check on his assignments every night, since he still has a tendency to "forget". Unfortunately, this is pretty time-consuming and if we don't do it for some reason, my son of course starts to slack off.
As for the video games, my son is addicted to them and it is really hard to enforce the time limit--he may get off of one thing for a while (computer, nintendo, game boy) but then he'll get back on something else (long time in the bathroom with the gameboy). Any suggestions?
As for the disorganized rooms, it drives me crazy! When my son was younger, he would cry and cry when he had to clean up his room. I took me a while to realize that this truly is a very difficult task for him. (We didn't realize he had ADHD until a few years back because he can spend enormous amounts of time and concentration on tasks such as legos, etc., that interest him.) I also have a husband with the same problem, a daughter with ADD & OCD, and it's too soon to tell about the youngest two. I am by no means a neat freak, but the constant clutter drives me up the wall as I seem to be the only person who is able to organize and pick up.
My kids (and husband!) are wonderful, really great kids, but it can be very exhausting!
Leigh Ann