If you want to print from any PC on the network, without any other PC having to be turned on, you need a print server.
I've no personal experience of home use of one of these, but
Edimax do one. The PS-1206UWg / PS-1206PWg, depending if you need a parallel or usb port. There's a list of printers that it's been tested on on the product page...
About £30 I think...