Be forewarned that porting apps to Android can be, at times, frustrating even for experienced developers. Not to discourage you -- just to let you know that you should have your guard up, and be prepared to do some fiddling before getting it "right."
The main thing you will need is the Android SDK -- this is what will allow you to access the Android system libraries, as well as run apps within an emulator (though testing with an actual Android device handy is highly recommended). Link: http://developer.android.com/sdk/index.html
Note that you will need both the "starter" package; and at least one of the SDK "version" packages. (Note that OS versions are to some extent backwards-compatible, so if you want to write an Android app that will work on a device with Android OS 2.0 or higher, you would use the Android 2.0 package -- your app will work with Android 2.0, and still run on later versions of the OS, theoretically.)
There's also extra steps (and lots of good resources) listed on the page linked above, so I will refrain from reinventing that wheel any further (unless of course you have more questions or run into any problems -- in which case, the hammer and chisel will be put back into action).