What you need is (depending upon your connection) a cable or ADSL modem connected by cat5e ethernet cable to a wireless/wired router (Linksys is decent kit). They connect to the WAN port. Most wireless routers also have a number of ethernet ports (4 normally) for wired connections to them. This gives you the option of connecting each pc to the router by wireless or ethernet cable.
An ADSL modem uses normal telephone lines for the connection to the internerd. Cable as you know uses fibre optics. ADSL performance is limited by the distance between yourself and the local exchange.
Then for each pc you need a pci wireless network card (forget the USB wireless dongles cos USB uses loads of resources and isn't fast enough unless you have USB2 ports on your pc). A typical pci wireless network card costs about £20-25.
As long as the pc is reasonably modern and running Win2k or Xp then it will cope well enough with a wireless card - if it's old and running Win98 then stick with a normal wired network card which can be connected to the router by ethernet cable.
Install each network card in each pc. Do the usual installation of drivers and configure each wireless nic (network interface card) for DHCP in its network properties.
Configure the wireless router as a DHCP server so that it hands out i/p addresses to each pc.
Specify the MAC addresses of each pc to be connected in the relevant router setup - this will ensure no outsider can use your connection.
Bish bosh - sorted.
One thing you should do for best performance is ensure that the wireless network cards or adaptors are of the same make and model range as the router. i.e use Linksys cards with a Linksys router or Belkin with Belkin as there can be interoperability issues with a mix and match approach.
I'm sure others can fill in the details to make this outline more comprehensive.
2 cylinders are all you need but, 3 is a fine compromise www.twpd.co.uk www.twpdracing.com