How does one get money into the Ripple system? There appear to be ways how one can lend various currencies in the system, but how does one get non-debt money into Ripple?
Fiat currencies can only exist as debt. If you have them, and they're not in your physical possession, it can only mean that someone owes them to you. This is the same way it works outside the Ripple system. If you have $1,000, and you don't have physical bills, then someone (most likely your bank) owes you that $1,000.
The Ripple system uses gateways whose primary purpose is to offer debt with "withdraw on demand" agreements with large numbers of people. This allows those people who are willing to trust that gateway to use their debt as a means of exchange. The Ripple system includes automated exchanges between gateways just as it provides exchanges between currencies.
This is analogous to conventional banking. If my bank owes me $100, I can send you a check to make your bank owe you $100 more and my bank owe me $100 less. You consider me to have paid you $100 because I made your bank owe you $100 and you chose to trust your bank.