1 : Unpack and upload the files into the folder : /plugins/topicsplitter/

2 : Go into the administration panel, then the tab "Plugins", click the name of the new plugin, and at bottom of the plugin properties, select "Install all".

3 : Then in the same page, check if this plugin require new tags in the skin files (.TPL).
If yes, then open the skin file(s) with a text editor, and add the tag(s).

4 : Some extended plugins have their own configuration entries, available by clicking the number near "Configuration" in the plugin properties, or go directly to the main configuration tab, section "Plugins".

5 : Save this image to your skins/.../img/system/ folder :

6 : Add this code in forums.posts.tpl, somewhere near the tag {FORUMS_POSTS_ROW_ADMIN} :

Code:
<a href="plug.php?e=topicsplitter&amp;id={FORUMS_POSTS_ROW_ID}"><img src="skins/{PHP.skin}/img/system/icon-split.gif" alt="Split"></a>