Installing and setting up the SDK environment for Mac is quite easy. All you'll need is a good internet connection and some patience. Maybe a beer and a double rainbow. Yes, why not?
Before starting, I recommend you to favorite the Android Developer Website. A good amount of ressources, links and advices are referenced there.
Downloading Eclipse Classic is your first step. Unzip and move the new folder into /Applications.
Second step: download the Android SDK. Place the new folder wherever you feel comfortable. Since I develop sometimes with xcode, I'm using the location /Developer/SDKs. Go to tools/ and launch android. Select Available Packages and install one of the SDK Platform (I personally installed v2.1). Close the application.
Third step: open a terminal and edit your .bash_profile, add in your PATH the directory of the Android SDK followed by /tools. You should have something like:
export PATH=${PATH}:/Developer/SDKs/Android-SDK/tools
Forth step: launch Eclipse. Go to Help > Install new Software. Add the address: https://dl-ssl.google.com/android/eclipse/. Install the Android Development Tools (ADT). After the restart, go to Preferences > Android. Insert the address of the SDK (without tools). After clicking on "Apply", it should display the Platform(s) you've downloaded previously.
You're ready to create your first Android project. There is a good Hello World article in the official documentation. Enjoy!