@Joomla_Direct Yes, Captions is compatible with Joomla 1.5. A new version will also be released this week.
Install or Update JCE MediaBox
Installing JCE MediaBox for Joomla! 2.5
Installation may fail on some servers due to technical limitations and a manual installation may be necessary.
For help installing Joomla! components, read the Joomla! Component Installation article