Decide on who you are goin to have your broadband with before you buy you're router. If you're getting it with a company that uses your telephone line, then you will need a router with modem built in. If the company has to put you a line in (i know blueyonder does) then you will need a router (without modem built in)
also depending on the distance between your router and your computers decides on the speed of the router you buy:
G = 54Mbps - probably do 2 rooms max each way
G+ = 108/125Mbps - almost double the distance of G
Pre n / draft n = 250Mbps+ - will definetly cover your whole house (and some of next doors house too!)
Once you have decided on the router you want, get the network cards/usb dongles that match that speed. eg. if you get G+ router, get G+ network card/usb dongles.
About the printer, you can either connect the printer to one computer and share it, or you can get a print server (wireless or wired) to connect it to the router. Both have good points and bad. If its shared from one computer then that computer has to be on for any other computer to print from it. If its connected to your router with a print server, any computer on that network can print from it, but that way is a bit more expensive and tricky to set up.
good luck!
