Buy the book "Isometric Game Programming With DirectX 7.0". It's old, but it's the only comprehensive book about the subject. I believe "Killer Game Programming with Java" also has a chapter about it, and the chapter might be available for free on the book's website.
Both books should be cheap.
Do a google search for free resources if you like. Here are my bookmarks about the subject:http://www.gamedev.net/reference/articles/article1800.asphttp://www.gamedev.net/reference/articles/article747.asphttp://www.java-gaming.org/topics/isometry-mouse-mapping-screen-to-worldcoordinates/16936/view.htmlhttp://www-cs-students.stanford.edu/~amitp/gameprog.html
I can't recall how good or bad the content was, but the fact that I bothered to bookmark those urls suggests that there must have been something good about them.
Since you're not so good with graphics at this point, you might want to focus on that first.