Ive done this in my 2003 dynamique. You have to take out the plastic tray, by undoing a screw. To access the screw, pull the seat forward and you can see it. Once the tray is out you need to get a bracket from Renualt, which costs about £12. My Sony Changer didnt fit in the predrilled holes (I think they are for an Alpine unit) so I drilled some more. The bracket just fits back in exactly the same place as the tray, with the same screw.
The wires are easy. I taped the two cables together and fed them under the kickplates. You dont have to pull them off completely, there is just enough room to get your fingers under.