First of all you either need a 205 with power steering fitted or read the 'how to' on converting a non PAS car but disregarding information about the pump, brackets & reservoir.
So first of all you will need all the relevant parts to complete the conversion:
1. Electric PAS pump (mine is off a Saxo)
2. Bracket for pump
3. Wiring loom
4. Pipes (High & low pressure - explained later)
5. New alternator belt (non-PAS)
I bought my pump second hand and it cost me £90 with a three month warranty. That included all wiring and relays etc… New the pump alone costs approx. £380 + cost of bracket, reservoir and wiring. The second hand pumps are a good buy as the Saxo/106 is a new car so parts on them aren't that old - mine was a year 2000.
I chose to mount my pump in the same place as it was on the Saxo (on chassis leg in front of gearbox). Since that has captive nuts in the leg I chose to weld my bracket on. It needs a little modification by cutting off a protruding plate that hits the crossmember. Also the radiator ideally should be tilted forward to give it more clearance as you don't want a hole in it when the pump moves (it sits in a rubber mount!) I just cut the lip off the cowl and the bottom right lug off radiator and it sat fine giving enough clearance. The radiator was then held in place by a zip tie in the bottom right and by all the other mounts.
Once the pump is mounted you need to connect the pipes. First low pressure return pipe goes over the small inlet into pump. Now the pump has been relocated the high pressure pipe (metal & rubber) wont fit. I got one made up at a local hydraulics place for £25. This involved me taking the pump fitting and rack fitting in to them and they made a pipe between the two ends out of rubber. Once that is done fit that and the only other connection is for the reservoir. This comes straight up from the pump and can be bolted to the front panel.
Now all that is needed is to wire it up. If you got the complete loom then there should be a two wire connection to the pump, a live, an earth and a small green wire (ignition live). These all go into a fairly large grey relay which can be tie wrapped behind the headlight.
That is it then - fill the system with fluid then turn the car on and bleed it up as in the Haynes manual. If you had PAS before then you will also need a new alternator belt - non PAS type. Then you have a very modern system that is especially useful when using carbs or similar as the belt driven pump will no longer fit properly.