Cannot "Install New Software" in Eclipse 3.5

GDK_NATIVE_WINDOWS=true also solved the non-clickable button problem for me running gnome 2.28.1 with Ubuntu Karmic (9.10) x64 with kernel 2.6.31-14-generic

I had the same problem, took a look at the error log and changed the launcher from "/usr/bin/eclipse" to "sudo /usr/bin/eclipse", it was a permissions thing...

Start by checking you error log under Window -> Show View -> Error Log. See if you're getting any exception while trying to install new software.

You can also install by downloading the plugin and unzipping it in the dropins folder.

I ran into the same problem. There seems to be a bug related to the finish button (I am assuming this is the same problem you are experiencing). The way I got around it is by clicking on the finish button (or next, or whichever button is not working for you) and press the 'Enter' key. It's annoying. Seems to be an issue with how Eclipse is integrating with GTK.