Something like a Netgear DG834G wireless/router/firewall/modem all in one is what you need.
click here (£104 at the moment, also 10% off offer at the moment)
Plumb router into phone socket. Then get cards or adapters for each pc. These can be in the form of usb drives, pci cards or external adapter for desktops. You can leave the router on, then just turn on the pc you want to use. If you connect your modem up to a pc, you will need that pc on to use bb on the others.
A data sheet for the DG834G (explains and bit about everything and what the firewall can do)
Get a filter for each phone point. I've yet to find any cheaper than these for £1.17 (used them lots of times setting up bb connections for people) click here
For the printer set up sharing, and as long as the pc connected to the printer is turned on you will be able to use it.
For arguements about 11mbps or 54mbps click here The speeds are theory, but if you are wanting to share files between pcs get the faster you can.
click here for comparing broadband. Personally use click here 2mb for £37.50 inc vat