Figure 3 shows that the Wi-Fire literally is a USB 2.0 WLAN adapter connected to a high-gain antenna.
Figure 3: Internal view in enclosure (click image to enlarge)
Figure 4 lets you see that the adapter uses a TI chipset consisting of TNETW1450 BB/MAC, TNETW3422 Direct Conversion Radio and TNETW3426 radio frequency front end.
Figure 4: Board and antenna detail (click image to enlarge)
The Wi-Fire's spec sheet says the antenna has 10.4 dBi of gain, minimum receive power of -98 dBm and +15 dBm (32 mW) of transmit power. The transmit power and receive sensitivity aren't anything out of the ordinary, so it's up to the antenna to provide the range-boosting mojo. hField doesn't provide any information about the antenna coverage pattern, but directs the user to point the leading edge toward the signal source. I thought this was an unusual orientation for a panel-design antenna, but my experience during testing generally confirmed this advice.
Update 11/12/2006 - A few readers wrote to tell me that the antenna is a Yagi, not a panel. That would account for the instructions to point the edge toward the signal source.