@Joomla_Direct Yes, Captions is compatible with Joomla 1.5. A new version will also be released this week.
Install or Update a JCE Plugin
Instructions for installing and updating JCE Plugins (Captions, File Manager, Media Manager etc)
If installing JCE MediaBox please see Install JCE MediaBox
From the Components menu click on the Install Add-ons item
Click the Browse button to locate the JCE Plugin Package eg: jce_mediamanager_204.zip on your comupter then click the Install Package button to install the plugin
A message will be displayed with plugin information when the plugin has been successfully installed