NEW YORK (CNN/Money.com) - Investors cheered Microsoft (Research) last week after a solid earnings report. Now, analysts and investors will be watching to see if new product releases this year from its two biggest cash cow franchises can help Microsoft keep up the momentum.

The crown jewel in Microsoft's spate of new products for 2006 is Vista, the first upgrade to its Windows operating system since October 2001 and set to hit the market in the last half of 2006. Microsoft chairman Bill Gates demonstrated Vista at this year's Consumer Electronics Show, the first time the public has seen the new operating system's features.

Vista represents a big investment for Microsoft, since it is the franchise product in the company's operating system division, which delivered $3.46 billion in sales in the fourth quarter alone.

Shares of the company, which have mostly traded in a holding pattern in the mid- to high-$20s for the last three years, started trading higher than they have all year following the release of its third quarter numbers, which also included a better than expected forecast. But analysts and investors are divided on whether Vista represents the catalyst for change that will drive Microsoft's long-dormant shares even higher.

Proponents say it's just the spark Microsoft needs to juice sales and perk up the stock price.

Analysts from Goldman Sachs agreed, writing in a research note that they expect Vista to generate between $1 billion and $1.5 billion in revenue in the first 18 months of its launch, which they expect will be in October.

"Vista should be a significant driver of both top-line and bottom-line growth," the analysts wrote. They offered "five compelling reasons" why users would want to upgrade to Vista, including improved security, aesthetics, enhanced multi-media capabilities and a more appealing platform for software developers.

But critics say Vista's new features aren't enough to inspire the kind of buying frenzy that once came with previous upgrades, such as the Windows 95 operating system, which generated a billion in revenue over an 18-month period after its launch 11 years ago, according to research from Goldman Sachs.

These people wonder if Microsoft will ever return to the days when upgrades to its operating system were hotly anticipated -- such as the Windows 95 release, "when people camped outside stores like it was the newest Harry Potter book," according to Brent Williams, an analyst at Keybanc Capital Markets.

Williams said those kinds of expectations came in part from savvy marketing, but also because each new Windows upgrade represented a dramatic leap forward in performance capabilities -- a feat that is becoming tougher as software becomes more and more complex and harder to build.

"The initial conception for Vista was to be exactly that kind of dramatic leap forward on a number of fronts," said Williams. "But we're 10 years further down the boulevard of history. The software is incredibly complicated to build."

Piper Jaffray's Munster thinks 2006 and the first half of 2007 will present the best opportunities Microsoft has had in the last four years to accelerate growth in revenues, thanks in part to the releases of Vista as well as Office 12, its suite of office software products.

"They've got to do it this time," he said. "This is it. The catalysts are clear."

He said that in the near term, a greater availability of its supply-constrained Xbox 360 console and the release of Office 12 will drive revenue growth. But in the last half of the year, the company will start making serious money on Vista, he said.

"2007 starts the rising tide of people slowly moving over to Vista," said Munster. "That will have a progressively stronger impact in '07."

Kim Caughey, vice president and senior analyst at the Fort Pitt Capital Group, which manages $825 million in assets, said while Vista will enhance Microsoft's visibility, she's not sure if it will carry a near-term pop the way past releases have.

"Vista will be much more secure, stable, incrementally better and visually exciting -- but I don't know whether it's going to be (a case like) Windows 3.1, where everybody went out and bought new hardware so they could get it," she said.

Keybanc's Williams added that consumers are unlikely to buy an upgrade package that would allow them to install Vista on machines they already own. That means Microsoft will have to get consumers excited enough about Vista to convince them that it's worth buying a new machine.

"You have to get consumers revved up about how great this is," he said. But he added that in so doing, Microsoft could be shooting itself in the foot, since presenting Vista as dramatically different could actually frighten away corporate users."

Analysts from Directions on Microsoft, an independent research firm devoted exclusively to tracking Microsoft, agreed with that assessment.

"Windows Vista could offer large organizations improvements in software development, security, reliability, systems management, and user interface," research director Rob Helm wrote in a recent note.

"However, public demonstrations have been full of cool graphics effects and consumer features that probably turn off more IT staff than they attract, and sales of Windows upgrade rights to corporations have been disappointing."

Helm believes that to sell Vista to corporations, Microsoft has to include features within Vista that appeals to corporate enterprises, explain clearly what those features are, and outline what hardware and other infrastructure companies need to reap the benefits of Vista.

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Disclosures: Keybanc's Williams does not own shares of Microsoft, but his firm has ties to the company. Goldman Sachs' Sherlund does not own shares of Microsoft, but his firm does banking business with the company. Piper Jaffray's Munster does not own shares of Microsoft, but his firm makes a market in the shares.