XML is used in many e-portals for content feeds, etc., so it's very important to learn how it works if you're going to build your own e-portal. InformIT offers a number of good books for learning XML.
Whether you're building your own portal, using a portal builder product to build one, or outsourcing the whole build completely, it makes sense to talk over the issues involved in building a portal. If you want further information, I've set up a virtual group on Yahoo! and have a number of portal experts on standby ready to answer any questions you may have.