Just to correct everyone else who posted here, Dreamhost does not have an automated installer for Wordpress-MU. Regular Wordpress, yes, but not what you’re asking for.
Because you mentioned WP-MU and Plog, I’m assuming that by “multi-user bloghost system” you actually mean “multi-blog”. If you don’t mind commercial software, I’ve run Movable Type here just fine in the past. I’d assume WP-MU and most anything else will work as well, provided the basic requirements are met (PHP/MySQL/whatever).
If you want useful replies, ask smart questions.