Simple question, with not-so-simple answers. Janus and I offered some advice in a recent EDoc Magazine article.

As a practical matter, for the business user in most enterprises, working with both CMS and portal software typically means working with two very different interfaces. In our experience, integration can be quite difficult and, therefore, few enterprises succeed at more than very high-level linkages between the two systems. You can draw a clear line, as some have tried, by saying that the CMS is responsible for managing content and the portal for information delivery. This leaves an important grey zone for managers: Where do we place navigation, site structure, and content preview? Which search engine will we use? Where will we integrate diverse content sources? And so on...

There's no single way to pull this off, but hopefully our summary of your choices will help you decide.