It’s not often you can get ahead by standing still, but Apple could be doing just that based on the latest survey on computer purchasing by Rockville, Md.-based ChangeWave Research.

The data on planned purchases among U.S. consumers and businesses shows Apple with steady numbers and those of its competitors, chiefly Dell and Hewlett-Packard, declining.

Rather than surveying the population at random, ChangeWave takes its samples from among its own 15,000-member “alliance.” It also conducts similar surveys at regular intervals, providing historical data for comparison.

Apple’s numbers are essentially flat from the last survey taken in January (see charts). The most encouraging news is that in the consumer segment, respondents saying they plan to buy a Mac are up more than 50 percent from the March 2007 survey.

Now compare those numbers with Dell’s numbers. Dell laptops are down 2 percent and desktops 4 percent with consumers (32 percent for desktops, 28 percent for laptops. As recently as January 2007, 44 percent of consumers were planning to get a Dell desktop and 34 percent a Dell laptop.

Planned business purchases have fallen to an all-time low (32 percent for laptops and 32 percent for desktops). At its peak in August 2005 Dell’s numbers were 45 percent for desktops and 40 percent for laptops.

HP’s numbers also showed an overall downward trend, particularly in the consumer space, where they’ve dropped from 27 percent for laptops and 28 percent for desktops last March to 19 percent for laptops and 18 percent for desktops in the just-released survey.

Assuming ChangeWave’s data is indicative of general buying patterns, Apple’s earnings should hold steady through the current challenging economic environment. And the Mac’s U.S. market share should continue to rise this year in the periodic IDC and Gartner reports.

Other findings in the ChangeWave survey:

Leopard rules, Vista drools: Of the corporate respondents using the Mac OS X Leopard operating system, 53 percents said they were “very satisfied” with it compared with 40 percent for Windows XP Pro and a sad 8 percent for Windows Vista Business. Linux beat both flavors of Windows with 44 percent.

The survey also asked corporations about their plans to adopt Vista. Only 18 percent said they were not planning to “slow adoption of Vista,” while 26 percent they were “somewhat likely” or “very likely” to slow adoption of Microsoft’s newest version of Windows. And a remarkable 43 percent said they had no plans to adopt Vista in the next 12 months.

If Apple successfully breaches the enterprise market with the iPhone, it might ponder pitching Macs to businesses. The sort of widespread rejection of Vista evident in the ChangeWave survey could encourage corporations to consider the Mac alternative just as consumers have.

Mac desktops surge: In the portion of the survey covering PCs purchased in the previous 90 days, Mac desktops showed stunning strength among consumers, with 21 percent saying they had bought a desktop Mac. Not only did Mac desktops gain 5 percentage points from January, the number tripled – yes, tripled – from March 2007. (The Mac laptop percentage among consumers dropped 1 point to 16 percent.)

And a bit of bad news: While most of the data in the ChangeWave survey is positive for Apple, I found one troubling anomaly. Alone among PC manufacturers, Apple’s numbers in the segment in which respondents report which brand of PC they purchased in the previous 90 days tend to be about half what they are in the planned purchases segment.

For example in the November survey, 29 percent of consumers said they’d buy a Mac laptop in the next 90 days but in the current survey only 16 percent did so. The desktop numbers are closer (29 percent planned, 21 percent bought), but it’s still a significant gap.

Such discrepancies don’t appear in the data on other PC manufacturers. Back in November 31 percent of consumers said they’d buy a Dell desktop in the next 90 days; in the current survey 28 percent said they did in fact buy a Dell desktop.

The laptop numbers are almost spot on: 28 percent said they planned to purchase a Dell laptop in November; in the current survey 27 percent said they did.

Apparently, potential Mac buyers are more likely to change their minds than potential buyers of other brands. But why?

Did they see ads for bottom-of-the-barrel PCs and conclude Macs cost too much? Are they Windows users fearful of making the switch? Or is it something else?

Whatever the cause, it would behoove Apple to invest some effort in figuring it out. Those lost customers translate to lost market share, lost revenue and lost profits.