The 6.x-1.1-dev version of the TinyMCE module doesn't work when used in a CCK text field set to "unlimited" for two reasons. One is that drag and drop functionality provided by Drupal core's tabledrag.js causes the tinymce editor's iframe to be reloaded, resulting in it breaking. This module addresses that problem by altering the tabledrag behavior. While a CCK multiple text field is the most common use-case, this module also enables tinymce to be used in other scenarios that use tabledrag.
The other reason tinymce doesn't work well in a multiple CCK text field is due to integration problems with AHAH. This problem is addressed in a separate module: tinymce_ahah.
This module depends on both the tinymce module and the jquery_aop module.