Single Log In To Multiple WordPress And SMF

I have two wordpress installed. One is for http://blogs.boingblogs.com/ and the other one is for http://news.boingblogs.com/ I want those domains to load their own home pages. That’s why I installed them on their own databases.

But isn’t it possible to use more than subdomain on the same wordpress installation? Since I have not done much on the WordPress sites, I would not mind deleting one of the WordPress installations if it is better to (and if it is even possible) to put more than one subdomain on the same WordPress installation.

Either way … I would like when somebody signs up for an account, they are automatically signed up everywhere else. And when they sign in, they are automatically signed in everywhere else.

ALSO I have a SMF http://forums.boingblogs.com/

so when somebody signs up for an account, they are automatically signed up for the SMF, and all of the wordpress subdomains.

I also have MediaWiki. http://wiki.boingblogs.com/ but I doubt MediaWiki is compatible with SMF and WordPress.

Is any of this possible? Which is the best way to make it to where users are automatically signed in everywhere else?