Details of the interface
This is how to wire everything up :
This is the pinout of the parallel port, as seen if you look at the 25 pin female connectoer on the outside of your computer
So pin 2 to 9 carry the 8 data signals in the parallel port and should be connected to the pins on the two 4066 IC's that control the switching. Those pins are the ones that the green lines in the schematic above connect to.

In the parallel port all the pins from 18 to 25 are ground an any one of them should be connected to the - terminal on the toys battery compartment, which is also connected to pin 7 of both the 4066 IC's. The rest of the pins in the parallel port is not used. Pin 14 of both 4066 IC's are connected to the + terminal on toys  battery compartment.
As already mentioned the core part of the interface is the 4066 IC. Each 4066 IC has 14 pins, four control pins, 4 pairs of switching pins , and 2 pins for power supply. Each control pin can turn one of the switch pairs on or off. Pin 14 is for the positive powersupply and pin 7 for ground.

As you can see the control pins are pin 5, 6, 12, 13.  These pins work at "the logic level" that just means that they are either high or low, high meaning at +5 V, and low meaning +0 V. In other words if you apply +5 V to pin 13 then pin 1 and pin 2 will be shorted together, and the same goes for the rest of the control pins.

Now this is very practical, because the data pins of a computers parallel port work at exactly the same logic levels, +5 V for high, and +0 V for low. That means that you can connect the data pins from the parallel port directly to the control pins of the 4066 IC. As luck is the high / low status of the parallel ports data pins can fairly easily be controlled from software. The parallel port has 8 data pins so two 4066 IC's can be controlled.

That's all there is to it.  Two 50 cent IC's and you can control 8 switches.

I'm absolutely no electronics guru, but as far as i can understand the spec sheet of the 4066 it's switches can only control voltages up to Vss, and max 20V. This means that the voltages you are switching with the 4066 must always be less than or equal to the supply voltage to the 4066, AND NEVER EXCEED 20V.  For your own saftey and the safety of your parallel port i suggest that you follow the general guidelines of circuit bending stay under 9V and never use stuff connected to mains voltages not even with a wall wart.

Here's an overview of the interface :

 
Disclaimer :

I build a couple of these interfaces, i have had them connected to several different computers and until now i have not damaged anything, but if you use this design it's at your on risk. Most modern computers have the parallel port embedded on the mother board so if it fries, you might have a very expensive motherboard repair.

I have a couple of very old and outdated Compaq notebook computers that was going to be thrown out at the company where i work and i use them to drive the interface. The sequencer program i have written will run on anything from Windows 95 and up, so most old computers should be sufficient.
I chose to build the interface in to the controlled toy. You could just as well build a stand alone version of the interface, and use it to control different toys, or maybe more than one toy at a time.

If you do the interface should be powered from a ca. 5 V source. I tried with 3 AA batteries i.e. 4.5 V and that works fine.
Here's a couple of pictures showing the interface and the parallel port connector. inside the Habitat Intercom
Theres a lot of wires going to the the interface, 8 from the parallel port and 16 to the switches, and to to the battery compartment, i strongly recommend a consistent use of colored wires. If for instance you use yellow wire from pin 2 (D0) on the parallel port to pin 13 on the first 4066, then you should also use yellow wire from pin 1 and 2 on the first 4066, the two pins that make up the switch that pin 13 controls. This way any troubleshooting will be a lot easier.
MikMo.dk > Circuit Bending > Schematics > Computer interface > Details