Yes, fitting an ethernet card is very easy and cheap. Cards can be had for about £5 and it takes longer to get the PC case off than to fit the card. I would say it is probably the least 'scary' job on a PC.
How old is your PC ? As my old (1998) unit had an ethernet port in it.
You will still need a router if you intend to have net access with the main PC off. You may also find that using an ethernet cable with the laptop becomes a pain especially when you forget and walk out the room with it.
I use 2 homeplug devices to connect the boy's PS2 upstairs to the router downstairs but at least Nintendo have sorted that issue out on the Wii being wireless.
Unless your house has very thick walls or is very large you should have no problem with wireless, but homeplugs are literally Plug N Play and so very easy to get going.