Here's another tethering app for the iPhone MyWi it turns the iPhone into a wireless hotspot. Unlike PdaNet or the config to enable native tethering available at http://help.benm.at/help.php, MyWi lets multiple PC's to connect to the iPhone for internet access. There is also no additional software to load for usb tethering.
MyWi supports wifi, bluetooth and usb tethering, it can even do both usb and wifi at the same time. Letting the iPhone charge while with multiple connections.
Okay now for the bad news it cost $9.99 and is available from http://www.rockyourphone.com/index.php/mywi.html on jailbroken iPhones, not a bad price if you need to use iPhone as a hotspot.