Movable Type looks just like what I'm using: APC Action Apps (http://www.apc.org/actionapps).
AA uses PHP and mySQL and it has email notification, public discussion/comment capability, user management, etc... everything it looks like MT has. (In fact, the latest developers' release has a Rich Text editor for the form fields your authors use when adding items to the site. It feels to them like they're using MS Word, not filling out a html form...)
I've set up a couple of sites with it, so I'm not sure if you've set up site management apps like this before, because it can be really tedious. (You'll also need PHPLib, and Dreamhost requires you to run your PHP scripts as cgi-php --it's an easy fix, though, with a .htaccess file. But Dreamhost support was very responsive when I needed their advice.)
Check out one of my sites, maintained using Action Apps,
The Robert Beck Memorial Cinema
AA also has a demo site, try out the features,
For the maximum amount of information, and the CVS info to get the latest developers' release, go to their SourceForge page,