everything is wireless with the exception of the readynas. I am also going to use a wireless extender which the readynas will be plugged into rather than the main router as the signal is quite weak at this end of the house
Assuming the router has wireless and 4 LAN ports.
Connect what ever possible via the LAN ports using Cat5 (Cat5e if Gigabit) cables, so that will most likely be the desktops and the NAS.
Set the desktops to Obtain an ip address automatically (DHCP) and they should see the router and therefore the internet and each other.
Log onto the router, often 192.168.0.1 and activate the DHCP server if not already on and set the Wireless settings (password).
Personally I would set the NAS with a Static ip, it'll be easier in the long run.
I guess the laptop would be wireless. So just let if find your wireless network and put in the password you set.
Simple enough really.
Doh, you typed this while I was typing!
I'd advise you to connect via cable where possible, you'll notice the speed difference for sure over wireless especially if your having signal issues.
Unless you are doing on-the-fly recoding of video, a media server only needs a low powered CPU in it. Mine is an old AMD Athlon 630 and that's way overspec'd and is probably handling a lot more than most peoples servers...You could use the main / most powerful PC as a media server that's what I've done it works for me
If you possibly can, run a cable from one end of the house to the other and make sure your router is gigabit - power line adapters rarely get above 100Mbits/sec which is really slow compared to gigabit (you WILL notice the speed difference if you are reading/writing files to the NAS). To me, network infrastructure is one of the more important things to spend a bit of money on (trust me, been cheap and then bought again!).