Copying is the problem, lending is not.
I propose software based on napster but with software
locks.
If I lend a mp3, my copy is locked and the lenders
unlocked.
If I request a file that I don't have and that file can be
found and locked, I get a copy. This is the equivalent to a
lend.
The
software could tag files that can't be locked such as
ones on mp3 players. Open copyable files could also have a
tag.
Files most requested would have to have enough bought
copies to service needs. If I buy a track I would be adding
to the global library.
There will always be theft, but most people want the fair
ticket price.
Ultimately it comes down to having exactly what you want
when you want it Or having a greater than personal
amount of choice.