Drupal has some interesting Multisite configuration opportunities.
You can set up multi site installs for same code base, different sub directories, or different sub domains.
You can set up multi domains off the same code base.
You can use the same database with different prefixes. You can use the same database with some tables shared, and some tables separate prefixes. You can also use different databases.
Here is a config for Multi-Site, Single Codebase, Shared Database, Shared Sign-on for Drupal 5.x
Here is a multi site, shared database single sign-on module.
Here is the Drupal Multisite Group. One of the key differences between WordPress Multi User and Drupal Multi Sites is additional folders need to be added for Drupal. Also if you’re doing new domains you must start a fresh install.
If you have a multi-site sub-folder install you can simply use the multisite manager.

2 Comments
Thanks for this, because Drupal is so flexible in the way you customise it, it can quickly get confusing when it comes to what set up you want.
Hopefully someone will write a module to manage multi-site install on Drupal (since I’m not a good enough programmer to do it myself).
Just also wondering what Drupal template you’re using for this site? Is it a custom written one?
Do you have any solution to use multiuser with drupal? It doesn’t come with the system, I think it need to use a plugin for that. However, I still can’t find the plugin with multiuser posting content in one blog. please email me withyour kindness if you have solution. speedyeoh (A) yahoo.com