Pulling Wire Through a Central Vacuum System?

call -151 asks: "A friend of mine has a nonworking central vacuum system in her house and I was offering to help her use the tubing as conduits and pull cable to distribute her network throughout the place. Has anyone done this and have any advice to offer? It should go smoothly but I'm sure there are some things I'm not thinking about." Of course, not everone can expect to have a CVS (pun intended) in their own home, but this was just odd enough where it deserved a post. Anyone have any URLs that describe exactly what a Central Vacuum System is, and how it worked?