The problem is due to a "technical specs disalignment" between Xara and AlinenSkin developers. Alien Skin developers assume that Xara application write some entries in the registry during the installation. This of course does not happen. The Xenofer installation checks for one of those entries and if it can not found it, it aborts the installation.
Once I have discovered what it was checking for, I simply added those keys on the registry, and the installation run successfully.
You may create your Registry entry in notepad just copying/pasting the following text:
Windows Registry Editor Version 5.00
"XaraX Root Dir"="C:\\Program Files\\Xara\\Xara Xtreme Pro 5"
just take care of having "C:\\Program Files\\Xara\\Xara Xtreme Pro" with the double "\\" and reflecting your actual XARA installation folder.
Save the notepad file as "Xenofer.reg" and close the notepad.
Open the folder where you saved the file and double click on it. Answer YES to the question "Are you sure that you want to add the information....."
Explore your Xara installation folder (normally: C:\Program Files\Xara\Xara Xtreme Pro 5\Xara Picture Editor\PSplug-ins) and delete all files and folder related to "AlienSkin Xenofer 2"
Then you may run the AlienSkin Xenofer 2 setup package, that will run fine.
You will not have duplicated entries in the Xara Plugin combo.
Hope it will help.
Merry Christmas and Happy New Year