From PGC:
PGC Mailbag
Current List of Compatible Routers
Ah, the basics! OK, I'll break it down for you. At home you have two options: you can use a wireless router or Nintendo's USB wireless connection device.
Standard Wireless Router: Any 802.11b or 802.11g router should fit the bill, though apparently some have compatibility problems. Simply connect your DSL or cable modem to the router. (You may connect your computers with Ethernet cables or wirelessly). The wireless network should be visible within the Nintendo WFC settings menu and work with no configuration (unless you want a secure network).
USB Connector: You can think of Nintendo's adapter as creating a proprietary network that only Nintendo DS (and assumedly Revolution) may use. After installing the bundled software on your Windows PC and connecting the USB device, you can connect to Nintendo WFC through your computer. The PC may be connected to the internet through any means, including another wireless network. The USB Connector is a good choice for anyone who wants maximum online mobility or does not want to compromise their current wireless network's security. (Nintendo DS does not support WPA, but the USB Connector could safely relay the DS connection through a WPA network.)
Outside of the home, you can connect to Nintendo WiFi through any standard WiFi hotspot, though you may need to jump through hoops. For example, my school's wireless network requires me to register my handheld's MAC address. "Hotspots" rarely have WEP or WPA security features that require special passwords, since their purpose is to provide a readily available internet connection. Commercial hotspots that charge for service will invariably require a laptop to pay for service and the USB connector to share that connection with the DS. Since Nintendo and Wayport have teamed up, any free Wayport hotspot that normally requires browser authentication is compatible with Nintendo WiFi.
The official Nintendo WiFi site provides a convenient archive of hotspots around the world—except for Australia. Sorry Aussies, but apparently wireless standards are either kooky down under, or NAL once again cannot be arsed to do anything.
PGC Mailbag
Current List of Compatible Routers