The clock is ticking for Napster. On July 1, the runaway hit that's given millions of consumers an easy way to access a virtually limitless selection of music they otherwise couldn't - or wouldn't - buy from their local record store is scheduled to be reborn as a for-fee service that pays royalties to copyright holders.

The success or failure of "Napster II" will likely have a huge effect on digital-music business models to come. Meanwhile, the music industry is also awaiting the much ballyhooed summer launches of MusicNet - a RealNetworks-incubated company that is co-owned by and will include music from BMG, Warner and EMI -and Duet, a joint venture of Universal and Sony.

Not everyone, however, is waiting around for the next two-and-a-half months to see whether a legitimate business can be built around peer-to-peer technology, the architecture that allows people to download files directly from each other's computers. Several companies are already experimenting with subscriptions, advertising-based revenue models and even voluntary payments in an effort to capitalize on p-to-p's popularity.

Last week, about 10,000 beta testers got a glimpse of the new Scour Exchange, which plans to gradually scale up to about 400,000 testers. In its previous life, Scour was a Napster-like file-sharing program that also enabled the exchange of video and images, in addition to music files. It drew the wrath of both the recording and motion-picture industries because, although it made a point of striking licensing deals to distribute certain content, it did not compensate the labels and studios for unauthorized files that were being traded on the system. This time around, Scour Exchange is being run by CenterSpan, a former joystick maker that purchased Scour's assets for $9 million in a bankruptcy court auction in December. The company's goal is to turn Scour into a subscription-based service that traffics only licensed files.

Whether CenterSpan will be able to secure deals that give it enough of the right content - that is, the kind people are willing to pay for - is the $9 million question. Final pricing hasn't been determined and during the free beta test the selection of audio files is very limited and no video is available, although the company says it is in active talks with labels and studios to add more content. And instead of transferring files freely between peers, for now users download files - all in Windows Media format - from centralized CenterSpan servers. Marketing VP Andy Mallinger says that at this stage the company is merely "seeding" the system with files, which users will be able to share directly with each other later.

Mallinger says it's too early to tell whether Scour would be able to benefit from major-label projects MusicNet and Duet. Indeed, it's unclear whether either venture will be technically compatible with any of the p-to-p networks, although Bertelsmann, which owns a 20 percent stake in MusicNet, has said publicly that its adopted child, Napster, will be a customer. (Bertelsmann is funding the development of Napster's secure subscription-based service.)

Others are trying to show how the existing p-to-p networks can generate revenue without charging consumers. For example, iMesh runs banner ads both on its Web site and within its file-sharing client software.

A new Toronto-based company called Jive Technologies, which raised about $1.9 million in Febrary, is pitching a solution for filmed entertainment that includes television-like commercials that can play at the beginning, middle and end of streaming video programming. Targeted ads can be rotated each time a user goes online. The company hopes to work with p-to-p providers to promote widespread adoption of the Jive Player, which is simply a layer that sits on top of popular media players such as QuickTime or Real.

For content owners who bristle at relying on advertisements for revenue, there are yet other options. Former Virgin Records artist Toby Slater recently released a track in partnership with digital-rights-management firm TryMedia. Although TryMedia allows content owners to impose any number of restrictions on files, Slater chose to give away the song in the open MP3 format. Instead of charging, playing the track triggers a prompt to install TryMedia's DRM software, a relatively small and quick download at 700KB. Once installed, the track not only plays in its entirety but a browser window opens to Slater's Web page, where listeners can get more information, download other songs and make voluntarily contributions to Slater.

"The voluntary payments thing was a sidenote," says Slater, who has earned $145 through Fairtunes.com, a "virtual tip jar" site, and an undisclosed amount through Amazon.com's Honor System compensation program. "But for me, bringing people into the community is as valuble as the payment. It's really important to get people visiting my site."

Fairtunes CEO Matt Goyer says that while the idea of voluntary payments is a noble one, it's a better in theory than in practice. "We've had a hard time making a go of it," he says. "It's a nice thought, but until the artist embraces it and promotes it to fans, it won't take off."

Still, Goyer says he'll incorporate voluntary micropayment functionality into a Napster-like software client he's trying to set up in Sealand, an island off the shore of Great Britain. He's also developing e-commerce with Snarfzilla, a file-sharing application based on the Freenet p-to-p technology.

Freenet author Ian Clarke is also launching a business based on elements of his software. Uprizer, which just closed a $4 million round of funding from Intel and others, is still in extreme stealth mode, but Clarke is trying to distance himself from the piracy rap, positioning the company as a business-to-business play that provides content distribution infrastructure.

"You have to draw a distinction between file-sharing applications that are readymade for copyright infringement, and peer-to-peer as an architecture idea," Richard Koman, editor of Openp2p.com, the peer-to-peer portal of technology think tank O'Reilly and Associates. With the Uprizer investment, he says, Intel is taking "a very long-term view of what the Internet is going to look llike, and how they're going to provide the basic building blocks."