Steam coming from the vents of my 2006 Proton Satria

This sounds awfully like your car has a leaking heater core. The heater core is really just a smaller version of the engine's radiator, but is located inside the car (usually under the dashboard) and is plumbed into the engine's cooling system. The idea is that the coolant from the engine (which is hot) can be piped through to the cabin via the heater core and can heat the car's interior.

If this heater core starts to leak, however, the coolant inside it has to go somewhere (the passenger's side floor in your case) and the hot water leaking into the vents can emerge as steam. Don't ignore this problem, however, as the leaking heater core will soon deplete the coolant that is supposed to cool the engine. When that happens, you'll destroy the car's engine.