Napster and Microsoft will find it hard to challenge Apple's number one spot in the digital music market because they are unable to offer both the music device and the music store, according to a report in a UK national paper.

Jupiter Research analyst Mark Mulligan told the Guardian: "Microsoft may be disadvantaged in this area because Apple already has the market lead with its iPod product.

"At the moment the defining company is Apple and iTunes. The iPod is leading the digital music market as much as the iTunes store. If this pattern continues then people like Napster, who provide the online music store only, could have something of a problem."

Mulligan uses the following analogy to explain why it is beneficial to offer both store and device: "It is pretty much like a walnut dashboard in a car – you're not going to buy a car because you want a walnut dashboard, however it might decide which model you get."

The fact that music in the Windows Media Audio format will not play on iPods will be another potential problem for Microsoft, according to Mulligan. He said: "One of the huge assets Apple has got is the huge installed base of media player users."

"Microsoft is also disadvantaged because without a hardware media player, it is dependent on partners to get its music download strategy into profitability. They can't go out and push a Microsoft music service in the way Apple can as they would alienate so many of their partners," added Mulligan.

Napster will launch its To Go music subscription service later this month. The service uses Microsoft's new Janus technology in Windows Media 10 to enable Napster subscribers to download music to portable devices. Users of the service rent rather than buy the music they want. Napster is one of the first music download services to incorporate the new Windows Media update.