I'll reiterate what Tetsujin said above -- there is no perfect setup. It's all about developing the habits, and particularly the habits of mind. Nobody can tell you which tool to use, because it all depends, although the archives of the google group, the blog -- including comments, and this board have detailed discussions of the pros and cons of (I'm guessing here) hundreds of specific toys. And every last one of them has someone who absolutely hates it.

So, to turn your question around, what's not working for you about your current system? When you say you aren't getting stuff into the system, do you mean that you're failing to capture your stuff? Putting it out of mind once you've got it written down? Are you better at keeping track of some categories or types of stuff than others? Is tracking time a problem for you (remembering appointments, missing deadlines)? Or do you run into trouble when you change locations, when you're away from your files or your computer? I'm not actually asking for a list of answers which will lead to one solution -- but the more you think of where your own sticking points are, the more aware you'll be of what you need in a system.

You say you're a week into GTD, and you've already tried some very different systems. However, you haven't given it the time to really make a habit of it. Don't worry about whether your tabs are the ones you're going to stick with forever -- worry for now about getting everything down so you don't have to keep worrying over it, in whatever form has the least overhead for you right now. Get in the habit of doing reviews -- start with the next day's calendar items at the end of business (so you don't get caught unprepared for that early morning meeting tomorrow), and whatever you've written down at the end of the week. Don't worry as much about the back-burner stuff until you've got some habits in place -- "someday" doesn't have to mean this Friday at 11:00.

Learn to write better to-dos. The David touches on this when he talks about the fact that you can only do "actions" and not "stuff", but I don't think he gives it anywhere near enough attention. The best thing I've ever done for my productivity, regardless of the guru or book or system I'm flirting with at the moment, has been to look at my to-do list as a real piece of writing with an audience and a purpose. I try as hard to communicate clearly (not that I always succeed) when the audience is just me and my pocketmod as I would for a wider audience. Why? Because if I've really succeeded in getting whatever it is out of my head, I may need the detailed instructions.

And then I screw something up and keep on going.

(Oh, and my system: pen and paper for capture, because I can take it anywhere and I can never, ever remember anything I haven't written down. Lotus Notes for calendar, email, and reminders, because work requires it and so I was already using it. Plain text files wherever I can, because I switch between platforms a lot.)