Well... I've been reading some of Ralstons book. It's really interesting, but it's not exactly easy to assimilate, and without physical training to back it up, I think it might be a bit overwhelming.
It's true that the terms "center" and "grounding" is used in many different ways in Aikido across the globe. You can read a lot of books about it - some with the focus upon the physical training aspects - some that deal with how you can user 'centering' in verbal conflict. Some are good, and some are to superficial for my taste.
It all boils down to the fact that center and grounding is something you should experience - not something you can read in a book.
If your area dosen't have aikido then look for something else that deals with some of the same issues (by other names maybe). Tai Chi could be one.. I THINK some styles of Kung Fu would as well. Judo teaches a strong center and grounding in a very physical way. Any martial art should have some aspect that will get you going in the right direction. Some forms of Yoga and meditation would also be good for getting in touch with your center.
If you are interested in the more esoteric concept of grounding and your time and money permits, I suggest you consider going to a seminar. I haven't been to one of George Leonards seminars, but they sound interesting, and he would be able to give you some exercises you can do..
So... what's my point? I guess it is that you don't need Aikido to become centered, and that it will be difficult to learn about your center from a book.
I hope you find a path towards what you are looking for - and someone to help you walk it.