I've just tackeld this job on the laguna 2.0 RXE with aircon. Initially (and according to most web sites) I though it would be a dash out job. I managed to do it in 3 hours & by removing less than 10 screws.
Basically the blower unit & aircon radiator stops you from removing the old unit under the passenger dash.
I cut a hole in the blower unit cover which allowed sufficient space to replace the heater matrix. Sounds scary, but reqally wasn't a problem.
Start by first remove the cubby hole (not essential, but helps), the 2 screws holding the heater matrix in place, and the bolt holding the pipes onto the heater matrix.
Then drill a small whole in the bottom right of the black blower unit(being carful to only go in a few millimeters with the drill. You can the put a screwdriver in and feel around to see how much space is available to do the main cutting. Once you're comfortable with the amount of space and where not to cut, cut it open (I initially used a jigsaw, then tin snips). Replace the unit & glue it back together again with a heated glue gun.
Obviously this procedure should be done with care, but it saved me from an expensive and unpleasent repair job.
Stuart
Stuart, April 2005