First you will need broadband internet. This includes things such as DSL, cable internet, or FIOS.
Then you would need a wireless router. These can be purchased for $30-100. If you can wait until you buy the laptop, wait because many stores will package a router and printer for Free after rebates when you purchase a laptop. These routers are generally low end, but will suffice for most people.
Once set up you will be able to use your 360, Wii, DS, and laptop on the network.
[edit]
I will add a bit about security.
It is always a good idea to secure your network, so people cannot steal your bandwidth or any information off of your computers. There are (I think, there may be more) 3 main ways to secure your network: WPA2, WPA, WEP. WPA2 is still failry new, but is supposed to be the most secure. It's level of security is followed by WPA, then WEP. WEP is generally not advised to be used because of the ease of hacking the network. With the right tools (that are not hard to get) it can be hacked in <5 Min.
I would say to use WPA or WPA2, but you want to use your DS. The DS does not support WPA, or WPA2.; it only supports WEP or no security. This is a big security risk. Because of this it may be wise to purchase the Nintendo WI-Fi adapter (which will work for your DS, and the Wii).
Or if you have a couple of wireless routers you can isolate your computers from the less secure network, which is what I did. This is a little more complicated, but it works.
