Eclipse+ADT debugger not working

[LanguidLegend]

Note: I'm using Windows 7 x64 and Eclipse 3.7.1. I have also installed the Android SDK using their self-installing executable file (installer_r13-windows.exe).

So I've just started learning Android dev, but I'm having trouble debugging my projects.
I'm following along in an Android dev book (Professional Android 2 Application Development) and am trying to debug a simple To-Do List app that I downloaded from the publisher's site. However, everytime I try to "Step into/over" the super.onCreate(R.layout.main) code, I'm presented with a "Source not found" error - in this case, a failed attempt to find source file "Activity.class".



However, I've tried debugging other projects, each returning a "Source not found" error for a different source file. I'm assuming they are the source files contained in the Android SDK, but how do I find/access them?
I've zipped my To-Do List project and uploaded it if you want to see it.

Really stuck! Please help!