WordPress 3.0 Problem Resolved
The lasted version of the Podcasting Plugin is compatible with 3.0. Please update plugin before updating to 3.0.
If you upgrade to 3.0 first and it causes your site to fail please use ftp to install the new plugin.
Or optionally you can delete line 15 in the podcasting.php file.
/plugins/podcasting/podcasting.php
register_taxonomy('podcast_format', 'custom_field');