1) Download the plugin from this site
2) Copy it in /plugin folder inside eclipse installation folder and restart eclipse.
-- If this does not work out, copy the plugin.jar file in /dropins folder.
3) Use Ctrl + + (Ctrl and Plus) or Ctrl - - for the functionality.
-- On my machine (Windows 7, Eclipse indigo- 1.4.2), Ctrl + shift + + works for zoom-in and Ctrl - -
for zoom out.