You'll probably want to connect your Windows environment to the Internet to run Internet applications that are available only in Windows, such as Internet Explorer (which is required to access some web-based software). Because of space limitations, I've assumed that the Mac you are using to run Windows is already connected to and configured for your local network and the Internet via a router/hub and broadband connection, such as cable or DSL.
Because you've already connected your Mac to a local network and the Internet via a router/hub, you don't need to do anything with hardware or your Internet account; the Windows environment will use the same connection to the Internet that your Mac does. If your Mac is connected to a wireless network, getting Windows to connect to the same network is straightforward. Likewise, if your Mac is connected to a network and the Internet via an ethernet connection, the Windows environment can use that same connection. All you need to do is configure the Windows OS to recognize and connect to the network you've already established. After you've done that, Windows will be able to communicate with other devices on the local network and have access to the Internet.
If you need help connecting and configuring a Mac to local networks and the Internet, see my book Special Edition Using Mac OS X Tiger.