ERROR:Could not find a Joomla! XML setup file in the package

[Admin]

The error usually means what it says i.e. there isn't a valid XML file in package. I've come across this with some free templates I've downloaded where the XML file has either been missing or wasn't written correctly but would of thought purchased ones should be okay.

Only thing I can think of is that its a 1.0.X template and it needs legacy mode to be enabled to be installed on 1.5.X

Another reason if the files are not going to temp correctly that is the issue, not the installer. So I would say you need to figure out what is wrong in the xml file or in your environment that makes it that the files are not moving to temp correctly.

The idea that there is not information on how to make a proper xml file for a 1.5 template is just not correct. Perhaps you are confused and think that it must be called setup.xml?