In a conference call with financial analysts, Microsoft CEO Steve Ballmer said he’s very exicted about the enthusiasm in the market for Windows Vista, but warned that some of the pie-in-the-sky sales figures he’s seen for the company’s latest operating system release may be too optimistic. “People have to understand that some of the revenue forecasts I’ve seen out there for Windows Vista in fiscal year 2008 are overly aggressive.” Ballmer declined to provide specific sales numbers, but noted that lower selling prices for the operating system, conservative corporate sales as enterprises ease into Vista from previous versions of Windows, and software piracy may all contribute to lower-than-expected sales forecasts.

Ballmer also indicated what while he expects Microsoft’s operating systems’ sales to expand in developing economies like China, Brazil, and India, the the growth will be on a smaller base than what Microsoft experienced in earlier years in developed nations, and the prevalence of software piracy in many emerging markets may dampen sales growth, despite new anti-piracy technologies built into Vista.

Overall, Ballmer reported strong sales for Vista at launch—which began for corporate customers in November 2006 and for consumers at the end of January 2007—but that the company did not expect that surge to extend into the company’s 2008 fiscal year, which gets underway July 1, 2007.