I had the same problem with Eclipse 3.8 for Linux. The following solution from the FAQ page worked for me, and since it was completely platform independent, it could help on other platforms too:
1) Select Help> Install New Software ...
2) Add the update software site (by clicking Add ...) and enter http://download.eclipse.org/releases/indigo [change the last word according to your Eclipse] for the location.
3) After adding the update site, try installing Android Developer Tools again, now it should download all the dependencies.
Milan source share