WordPress MU

I only want certain people to be able to create blogs, while still allowing everyone to create subscriber accounts. I started creating a plug-in that would verify a password (or eventually an invitation code) but now I'm stuck on figuring out how situationally turn on/off the blog creation form.

I'm certainly open to other ideas too...

Well, what do you mean 'certain' people?
You'll manually specify who can create blogs and who can't?

A simple solution is Invites - http://wpmudevorg.wordpress.com/project/secure-invitations

If you also have BP - http://wpmudevorg.wordpress.com/project/wp-invites

For a sophisticated solutions - check these:

http://premium.wpmudev.org/project/pay-to-blog
http://premium.wpmudev.org/project/supporter
http://premium.wpmudev.org/project/upgrades

I'm looking for something along the lines of http://wpmudevorg.wordpress.com/project/wp-invites but only for blogs. I want everyone to be able to register as subscriber, but they need a one time use code to create a new blog.

I need that too : allow certain users to create a blog.

did you find a solution ?

thanks in advance