How should I approach teaching Magic:The Gathering to a new player?
Have to say, I hated Portal.  If someone can't cope with the word "block" (Portal used "intercept" instead) or the concept of playing a spell at instant speed, they're not going to get on with Magic in the long run.  So why even bother with a watered-down version?

Modern Magic Core sets, like M11, are pretty well designed so that they contain everything that makes the game great, while remaining pretty accessible to a beginner.  Sure, there are some moderately advanced concepts in the set... but they tend to be restricted to uncommon or rare cards.  The commons are pretty straightforward, and have important rules clearly reiterated on the cards, in the form of reminder text.  You don't have to worry about explaining at great length how Flying works: it says so on every common card.

Sure, Magic is a pretty complicated game. However, it's gotten a lot easier from the worst bad old days of interrupts, mana burn, damage on the stack and the subtle difference between "destroy" and "bury".  Anyone who can cope with Settlers of Catan shouldn't have a problem getting their head around Magic!  All you really need to explain is one land a turn, sorceries only in your turn outside of combat vs. instants at any time, and the fact that you have a window to do things after attackers are declared, and then after blockers are declared, and you've explained 90% of the "intricacies" of the game.  

Don't sell your friends short - let them into the full and wonderful game.  If you must simplify it, then build some decks with only simpler cards in them, and play with those, gradually introducing more concepts as you go along.  But I really don't think there's any call for Portalizing the game.  Anything that is in a modern Core Set has been proven to be "grokkable" even by beginning players by extensive WotC market research.  I think people respond better, in general, to you giving their intelligence the benefit of the doubt, rather than patronizing them with a vastly reduced experience!