how do you add new users to a public-read/private-write wiki?

Hi, we have prhistory.pbwiki.com (premium, education). We want public access for reading, but private for updating. I click on settings/users and add a new email address as a contributor. There new user gets the email, they click the link, it drops them at the wiki. They try to edit a page and are shown a two column login page: one side is asking for an invite key, which wasn't in the invitation (and which we don't want to use anyway), the other side is asking for an email and password to pbwiki, but has no link to make a new account or any explaination about why you would need/want a pbwiki account.

Tell me how to get this: I enter the new user's email address, when they click on a link in the message, they go to a page that says, "Howdy, to update the prhistory wiki, please fill out this form (login, pwd) and you'll have a wiki account to allow you to update, check your mail for a confirmation". Send them back to their email to confirm and then when they click on the next link in that message, drop them at the login page and allow them to login in.

Also, I noticed a place on the "Users" screen for listing people who have requested access to this wiki. What text do I put on my wiki's front page so that my users can just initiate the process of requesting access?

Thanks,
Kelly B.