Goto connect.apple.com and register as an online member. The registration is free. The dev tools are around 95 MBs so I hope you have a broadband connection. If you don't have a broadband connection then you can start the d/l at night and let it go overnight.
Applewatcher, at the risk of repeating myself overmuch, you would really be wise to search the previous posts (the search link is at the top right of the page...) before posting questions. It's all there, and you might get your answers faster.
The dev tools are so large because they include compilers, interface building tools, examples of code, documentation, and many thousands of other things which I haven't totally finished going through. You need a rudimentary knowledge of Mac or UNIX programming to use most of them. I don't condone rote following of directions posted on the web that one doesn't have at least a vague idea of what each command means, because a lot of these "recipe" type instructions require SU'ing, and a typo there could land you in a world or hurt, though usually nothing that a reinstall couldn't fix. (The plist editor is nice, generally useful, and really should be included on a standard install, though...)
AFAIK, there are no dock modifications that require the dev tools. You can change the background without them, you can make it show the foreground app and gray out hidden apps, all without the tools. There have been numerous posts about how to do these, and a search through past messages might have saved you a 70 meg download (if you've already done it.)
Good luck learning more about the new OS. It's a bit of a change, but I think it to be well worth it.