Just a few things I noticed should be cleared up.
As you can see, the system is similar to other Joomla! XML installation files. You only have to look out for the group="xxx" entry in the <install> tag and the extended information in the <filename> tag. This information tells Joomla! into which folder to copy the file and to which group the plugin should be added.
The XML is indeed similar to the other 2.5 Joomla XML Installation Files, however;
Also, would be awesome to see an end plugin there, or an alternative tutorial such as Creating a Search Plugin - Bladeoz