Mel as I understand it the difference between CMS (yes Content Management System) and a portal is a CMS site is content focused and a portal is people focused.

I am most interested in dealing with content so that is what I have focused on. Content meaning stuff you want to show on your web site. A wiki, blobs, small or large pages of info, list of links, downloads, things you have for sale with pictures in some sort of list navagable format, News Feeds etc....

However what seems to me to happen in open source is that things are borrowed and cross bread because someone has the time and desire to do it and this seems to happen all all over the place. Since both of these types of web apps usually allow for functionality to be installed in a modular basis it seems that modules are getting ported to both types of systems. Also other main stream Open Source Web apps like BBS's, News Groups systems, Help Desk apps etc are being turned into modules or components for CMS's and Portals. So both types of apps, portals and CMS's are becoming similar with features.

There are also similar needs in both approaches as well. In other words even though your focus is building a community around something you most of the time need to handle content and visa versa.

I really like Mambo and would reccomend a serious look into. At least to see how its all done.