Although the Internet continues to expand its reach at a dizzying pace, the network of networks is still more an information swamp than a superhighway. Most of what’s there is junk, and precious nuggets are too often too difficult to find. So last July, when the Vatican made 20,000 images from rare documents available on-line to scholars around the world, it might have been a small step for the Apostolic Library--which holds more than 150,000 ancient volumes, or millions of pages--but it was a respectable leap for the Internet. The Vatican collection is a fair-size digital library by Internet standards, says Fred Mintzer, a computer scientist at IBM, a partner in the project. Right now, there isn’t a lot out there.