Try going to your wp-config.php file and deleting these two lines:
define(‘DB_CHARSET’, ‘utf8’);
define(‘DB_COLLATE’, ”);
I had the same problem (it’s fixed now) and I believe it is because of upgrading from pre 2.0 versions to 2.2 through Fantastico.
More information is here.
Try the Chenpress plugin to get a better WYSIWYG editor. I can’t help fix the problem, though. This is why I rolled back to 2.0.7 and am waiting for them to fix 2.1.
Update: My guess is that this has to do with the sideblog plugin. I wound up rolling back to 2.0.7 because of other issues, but if anyone else encounters this, try upgrading your plugin.
In response to Xander, I did triple-check the files in my install. I wound up rolling back to 2.0.7 and installing FCKeditor instead of using TinyMCE. When I rolledback, the image browser appeared, but I continued to get javascript errors. My Chenpress plugin has solved the problem.
