I found using an old PC to be a bad idea as that's 100++++ Watts running 24x7. Today I'm using a simple 228 buck netbook from Walmart with a 250GB HDD. If I did have a larger collection I might get a few external drives on that.

But what you are looking for has never been made for reasons that should be clear. Why should Zune software work with Apple gear and vice versa.

For me the 250GB HDD is ample but some pirate content and can't deal with something that small. Anytime you read "I have 20,000 songs" you have to wonder how they sank 20K bucks into a collection.