"So, although total dollars were down compared to XP, I think the preliminary data shows that Microsoft's gamble on a new high-end Vista SKU will help keep dollar volumes from declining as rapidly as unit volumes in the near term," said Swenson.

Swenson also expects that retailers with "tech benches" such as Best Buy's Geek Squad, CompUSA's Tech Pro and Staples' Easy Tech will see a boost in sales because of customers seeking help with installing Vista. Those services are often offered at attractive prices to consumers, said Swenson, who expects a "bump" in sales similar to that caused by security software.

NPD's data was collected from a number of retailers, including Amazon.com, Best Buy, Circuit City, CompUSA, Kmart, Office Depot, OfficeMax, Staples, Target and others.