It was just showing the "Xtra Downloaded" window and that is it. I reset my machine and tried again and the install feature started working.

I've updated my blog and this page to hopefully make it clearer.

Clicking Install on this AdiumXtras page does not work for me. Plus just downloading the file attached to this site does not provide the *full* theme, just the look of the contact list. The instructions on the blog are for installing the full theme.