“We believe the teen demographic is a critical component of long-term growth in the digital music and mobile markets, and Apple is taking its lead in music and leveraging it in the mobile category.”

So writes senior research analyst Gene Munster in his summary of Piper Jaffray’s 20th bi-annual teen survey, which quizzed 6,000 high school students about the iPhone, iPods and online music. The results bear him out — to a point.

• 33% of teens surveyed plan to buy an iPhone within 6 months, up from 22% last year. “Historically, interest in buying an iPhone has correlated to future market share gains among teens,” Munster notes, “although the last two surveys have not shown the same share gains we saw when the iPhone first launched.” Indeed, the 14% who say they already own an iPhone is down from 15% in 2009.
• The iPod’s share of the MP3 market stands at 78%, down from 87% a year ago. Why the drop? Munster suggests it may be because 50% of students are listening to music on their smartphones.
• 76% of students download music — unchanged from last year — and most (66%) are still using free (P2P) file sharing networks rather than paying for their music. Among those who do pay, however, nearly all of them (95%) use iTunes.

Further evidence that Apple (AAPL) is winning the battle for the hearts and minds of American teenagers: when asked by Sam’s Club (WMT) which entrepreneur they admire most, nearly a quarter (23%) picked Steve Jobs. That’s down from 35% last year, but still ahead of J.K. Rowling (17%), Oprah Winfrey (14%), Jay-Z (13%), Mark Zuckerberg (9%) and Tony Hawk (9%). See here.

[Follow Philip Elmer-DeWitt on Twitter @philiped]