But I really wanted to be able to do it without the main computer being on - I haven't got a network enabled printer - it just has the normal printer ports (It's a year old Cannon thing) - is it possible to buy some sort of add on to make it a wireless network printer or do I effectively need to buy a wireless printer? Yhey seem very expensive....
You can by wireless printer servers. Small box similar to your wireless modem/router. Some wireless routers do have printer ports to plug non wireless printers into them. Lots of options, all are gonna cost between 50 and a ton.