It really is quite simple: You need to determine what sort of access you have to get the wires where you need them and you need to determine how you will power those speakers.
Typical setup:
1. A volume control in each room with speaker wire running through it by the entry way to that room.
2. A pair of speakers in each room with speaker wire running from the speakers, through the volume control, and back to the head end.
3. An impedence matching speaker selector box at the head end with all the rooms tied into it.
4. A decent amplifier in front of the speaker selector box to put out some power for all the speakers.
5. A source, or A/V receiver, tied into the amplifier. That's what that 'zone 2' or 'zone 3' output is for on A/V receivers!
How hard is it? Well, it is 100% dependent on your access! If you have an attic overhead and can just cut some round speakers into your ceiling, lay the wires across your attic space and drop the wire through the speaker hole you cut, connect it to a speaker, then put the speaker in the ceiling, it is likely a good weekend project - start to finish. You won't really need to snake wires all over your home or deal with patching a bunch of holes in your drywall.
If you opt to not use volume controls in each room, but put volume control at the head end, that simplifies things even further since you don't need to run the speaker wire down into an existing wall and find where the right studs are.
Electrical books can often help you find info on running wires since they are so readily available at your local hardware store. The main thing you need to do is run the wires. Cutting drywall and connecting the equipment is easy.