If the close button graphic and the "weblink" graphic are not displayed on all your pages using thickbox, you have to edit one of the following files (dependig on which plugin you use):

Thickbox for J!1.0.x	/mambots/content/includes/thickbox.js
Lighwindow:	/mambots/content/thickbox/includes/smoothbox.js
RSS Browser for J!1.5:	/modules/mod_thick_rss/includes/smoothbox.js
Thick RSS Browser:	/modules/includes/thickbox.js
Thickbox prototype ed.	/mambots/content/includes/js/ptthickbox.js

The "homepath" variable should direct to your Joomla home directory relative to server root (in Joomla terms: $config_live_site minus domain name)
e.g. if your Joomla homedir is http://<your-domain>/joomla ,
If Joomla root and server root are identical, homepath should be an empty string (default):

That's all you have to do.