Apple Computer is beginning a wrenching tectonic shift, taking its Macintosh computer line from IBM and Freescale Semiconductor’s PowerPC to the Intel Core Duo, two chip standards that have little in common – aside from a reliance on silicon and a vocabulary limited to 1s and 0s.

The change is so radical that existing Macintosh software could have become obsolete – if not for some near-wizardry. CEO Steve Jobs, always the showman, came to the Macworld Expo this week and unveiled two new Intel-based hardware products that have enthusiasts – and Wall Street – salivating. Analysts and rumormongers had been anticipating an Intel-based Mac since June, but it came as a surprise when Jobs announced not one, but two such products: a new iMac and the MacBook Pro laptop, the latter already shipping.

This rapidity was key, says Nathan Brookward, principal analyst of industry research firm Insight 64. “When Apple first announced the Intel switch in June, I was concerned sales of PowerPC Macs would slow and there would be severe software shortages for end users,” he says. However, now he believes the speedy hardware roll-out could “smooth the software transition.”

And there was more to Jobs’ announcement. The switch to Intel had raised serious questions about backward compatibility for Apple software that runs on the former PowerPC architecture. So Jobs also unveiled an application called Rosetta, which offers interface-free emulation to translate PowerPC code into Intel code on the fly.

This application was vitally important, because the fundamental differences between Intel and PowerPC architectures mean no Mac user’s library of existing software would run on an Intel-based Mac. Apple’s solution, at least until developers reconfigure their applications into Intel-native versions – a process that could be little more than a recompile or, for massive projects like Adobe Photoshop or Microsoft Office, a mammoth undertakings – is to use Rosetta.

Rosetta is not a perfect solution, though. Even Jobs admitted in his keynote speech that the application is not an optimal solution for professional users – some pro-level software, such as Apple’s own Final Cut Pro, Logic Pro and Aperture won’t run under Rosetta. And running an application under Rosetta means a drop in performance. But for everyday users, the new Mac is, well, a Mac.

Michael Gartenberg, vice president and research director at Jupiter Research, says that Apple has taken extensive steps so that “for Apple customers, the transition is almost seamless – it almost doesn’t matter.”

Certainly, the new Intel iMac looks identical to the previous model – Jobs stressed that it had “the same design, the same features and the same prices” as its PowerPC predecessor. Similarly, the new MacBook Pro looks almost indistinguishable from the PowerBook model it supplants.

Although the present seems to be about Macs being Macs, research analyst Gartenberg points out that the future may bring a change, given the similar strategic goals of Apple and Intel. “We know that Intel has designs on the digital home, the digital living room, and Intel has found a good partner in Apple,” he says. “It’s not about convergence anymore, but how to integrate TV with the other digital content that lives in a computer.”

For Apple, the future is about seamlessly marrying the two mediums. And now there’s more entertainment to share: Apple has led the way, making a much-publicized deal last fall with ABC and Disney to sell downloadable video content through its iTunes Music Store. Yahoo and Google, among others, have since made similar moves.

Even without a computer-to-computer network, Apple has a potentially killer front-end for content playback – something Intel has never managed to create. Apple has also debuted Front Row, which replaces the Mac OS X interface with a screen that can be viewed from across the room, and which serves to navigate and play movies, music, and other digital content. Indeed, Front Row, which ships with the new iMacs and MacBook Pros, includes a remote control. Some have looked at Apple’s ability to stream and sell videos, extensive and extending content partnerships, Front Row, and QuickTime standard – and seen a computer that can replace the need for a TiVo-like device.

Intel, for its part, is promoting its Viiv brand (tag line: “Change the way you enjoy entertainment at home”). A Viiv-based PC is supposed to meet minimum standards for remote control of applications, on-demand digital content, DVR, and other functionality. Currently, this requires Windows Media Center Edition; but given the new partnership with Apple, there’s no reason the same technology can’t go toward a media center Mac – especially with Intel designing and manufacturing Apple’s computer motherboards. (On the other hand, Apple may feel that Front Row makes this unnecessary.)

“The role of the PC is evolving,” said Gartenberg. “They’re not giving up their current role, but adding high-definition TV, music and more.”

It’s not clear that any one company could do this alone. But Intel has had billions of dollars waiting for a good idea – and Apple has nothing if not ideas.