Nintendo recently unveiled a new WiFi USB connector as part of their latest attempt to release a line of Nintendo-branded wireless products. As soon as you insert this dongle into your PC (no Mac-compatibility at this time — bummer), a window will open to establish a link between it and your DS. After going through three option screens, you'll be online. The dongle is jointly developed with Buffalo Technology, which will also release Nintendo WiFi Station access points to stores in Japan, to create instant DS "hot spots."
The WiFi connector dongle will go on sale in Europe in November for about 30, though there's no word on availability stateside.