Yes you can, there is a device that you attach to your PC to for Internet. The Wii connects to that device for internet and thats it. Your PC must be on and connected to the internet when ever you want the wii to connect.
No, it's a USB wireless access point. In other words it works like this:
1) You computer is connected to the internet
2) The USB adaptor software uses the computer connection for it's internet access.
3) The USB transmit a wireless signal for wirelss connection for the Wii
4) The Wii connects to the wirelss connection which in turns uses the software to connect to the computer active internet.
You could find it on Amazon or even on the Nintnedo website. Due note that the Nintendo version is the easy to setup and work with the Wii and DS. There are other USB WiFi but those are dependent on its software and requires you to configure it. As for the Nintendo USB Wifi, I'm not sure if its compatiable with other Wifi devices like IPhone and such but I do know it works for the Wii and DS as it was made for it.