The free version comes with the Open Source license LGPL 2.1 and is supported by the community.

http://tinymce.moxiecode.com/

This option enables you to specify a custom CSS file that extends the theme content CSS. This CSS file is the one used within the editor (the editable area). This option can also be a comma separated list of URLs.

http://wiki.moxiecode.com/index.php/TinyMCE:Configuration/content_css

TinyMCE's plugins at SourceForge

• homepage http://www.swampyfoot.com/swampybrowser
• at TinyMCE's plugins repo: http://sourceforge.net/tracker/?func=detail&aid=2722457&group_id=103281&atid=738747

• homepage: http://www.neele.name/filebrowser/
• at TinyMCE's plugins repo: http://sourceforge.net/tracker/?func=detail&aid=3005287&group_id=103281&atid=738747

Use TinyFCK, a mod that combines TinyMCE and the file manager from FCK Editor.

http://www.bram.us/2006/10/02/my-tinymce-file-management/