Bug Reports: Re: Members Edit permissions.
You aren't doing anything wrong - you can't grant contribute rights to an individual CMS page. It's something we've long thought would be good, but the main problem is that to edit a page you need to be able to access the admin panel for the site, which means a user needs to be a full administrator.
Hence there's no system in the CMS, currently, to have a user who can edit a page who isn't an admin of the entire site.
So - what I would probably recommend is that you use the weblog with permissions set so that members can contribute.
Then, rather than just submitting a link, they can add a link and bit of description/etc too.
For more info see: http://cambridgeopensystems.com/documentation/applications/noticeboard-weblog/