Interesting ideas, but I have more questions than suggestions, I'm afraid.
Linking P2P networks to content available on the WWW makes sense. Which P2P networks would you be using? Are you trying to make the metadata available in this index serchable by these networks? The problem you'll run into there is that most networks only search file names and ID3 tags. If a peer hosted a chunk of the index the network would only look at that chunk's file name and not the data it contains.
I guess I'm not sure why the index needs to be decentralized. If your server already indexes ~70,000 links couldn't it do more? If someone wanted to search for music on the web they'd probably prefer to use your website rather than a P2P network. Usually when it comes to web hosting the factor that limits scalability isn't computing power since you could always get more servers to do the job. That of course costs more in hosting fees which is what usually determines the maximum capicity of a given web site.
Nevermind, I think I just answered my own question. Decentralizing the index would keep the operating costs down to a minimum.
I guess to do this you would need two things: a server to compile the index and feed it into the P2P network, and a specialized client that is able to host, search, and redistribute the index to other nodes. Such a client would probably act a lot like Freenet. The network protocol doesn't need to be specialized as far as I can see, Gnutella would probably do the job. The only thing is that everyone would need to be running this client in order for it to work.
P.S. Welcome to NU, ormm.
