What is an Access Point? :P

You need either a Access Point or Wireless Router. Either one hooks up to your existing router and then you can get a wireless connection for your laptop.

think of an access point as the wireless equivalent to a hub or switch.  unlike a router it will not create a new network segment.  the previous post aside i recommend either buying an access point and plugging it into your current router/hub or buying a wireless router and replacing your current router with it.  there is no reason you want to have a router hooked into a router, and having a NAT network behind another NAT network can create problems for some internet applications/connections

Where would I be able to buy an access point, and how much?

:P I'm too lazy to order another exspensive thing online and then have to wait for it. I'll just go to one of the few computer stores around town, one of them must have one ;)

This is a very nice one ...  you can probably find a cheaper product ... check to find it online for sale

 

http://www.dlink.com/products/?pid=292

To be honest, most retail stores will sell wireless routers and wireless access points for around the same price.  It may be cheaper to just buy a wireless router and replace your current router.  You'll need to decide if you want 802.11b or 802.11g.  Use whatever your current card is.

Note, if you want to go the accesspoint route, bestbuy has an 802.11b one for $60

http://www.bestbuy.com/site/olspage.jsp?id=1051384240387&skuId=4086321&productCategoryId=pcmcat25300050001&type=product

but for that you could easily get an 802.11g router...   your call

But if I get a wireless router, won't I have to do something with the 3 other computers in the house? Wow, 4 computers.... >.>

most routers and wireless routers come with a 4port switch built in ....  thus if they're all hooked into the same box now it will be very easy to hook them into the new one

see, the problem is that nearly all routers today come with switches built in so people think that they're the same thing...  the same thing is kinda happening with "wireless routers," which are really a router, switch, and accesspoint/bridge all in one..