Since the progression of WordPress beyond version 2.5x, the Advanced TinyMCE plug-in has reached its E.O.L. A better alternative that is being kept current is TinyMCE Advanced
from Andrew Ozz
. Advanced TinyMCE is still available for download for older WP versions.
New WordPress Release Imminent
According to the WordPress codex, my Advanced TinyMCE Editor has been tested and found compatible with WordPress v. 2.3. (About 160 total plug-ins have been so verified.)
This new WP version adds enhanced support for tagging, among others (see Aaron Brazell’s 10 things you should know about this release).
I will be doing my own testing when a stable release is issued, but this is good news for this popular plug-in. You may get version 0.5 of Advanced TinyMCE from here.