Every time I tried to update the Android SDK on Windows 7 I'd receive a 'Nothing updated' error. Looking through the running log of the download there were multiple File Not Found errors. I ran into this when I tried adding in the nook color emulator URL as well.
If your screen looks like this, you're doing it wrong.
This issue is due to the inability for the SDK to access the Program Files (x86) folder on Windows 7 from the SDK Manager.
The quick workaround: Right-click on Android SDK Manager and Run as Administrator.