Wireless Networking for desktops

Hi, currently at my house we have about 5 desktops.  I was wondering how I can set up wireless networking the cheapest and in the most convenient way.  Will I need to get a wireless network card for each desktop, along with a router and some access points?  I've also heard of USB clients that can be used for wireless networking (currently using on my laptop on campus), which works fairly well.  Is it possible for me to use USB wireless networking clients on my desktops so I won't have to install each wireless network card for the desktops?  Also... what's the deal with access points?  Are they just there to ensure faster speeds because they're closer to the card? 

 

Thanks!