Hi, nice to meet you. Thanks for your comment on my piccies!!...Yes here in the UK we have many people riding horses, various disciplines etc...Dressage is getting bigger but more thought of by "Joe Public" as being a snobby sport!..How wrong they are as many of us are quite ordinary working gals and guys!!!...Show jumping I believe is still the tops as it has more thrills and spills for "non horsey" people to watch!!
For a comprehensive book on beginning dressage, try the USDF Guide to Dressage by Jennifer O. Bryant. It starts out assuming you know nothing, then goes on from there. Available at Amazon.com and larger bookstores such as Borders. As you get more familiar with dressage, you will discover that there are two (sometimes overlapping) approaches--classical and competitive. And there are fierce partisans on both sides. As with all things horses, there is an unlimited number of opinions. As you educate yourself, you can decided which style resonates with you.