PdaNet is a free utility that once installed both on your Mac and your Android PDA enables you to use your device as a USB modem (to "tether" it as it is commonly referred to). In this example I used the HTC Legend with a MacBook Pro running MacOS 10.6.2
On the Mac, download the PdaNet Desktop application from JuneFabrics - http://www.junefabrics.com/android/mac.php
Ensure that the Android device is not connected to the Mac via USB at this point.
Launch the installer:
Click Install, you will be warned that the installation will require a reboot of the Mac:
Click Continue Installation. The required drivers will be copied to the Mac. When complete, click Restart
Once rebooted, a new icon will be added to the Menu bar for the PdaNet application:
On the Android PDA, browse for PdaNet in the Android Market and download the client application. A new icon will be added to the Menu:
Connect the PDA to the Mac. A new network interface will be detected:
(NOTE - on most Macs the network adapter ID will be en2 or en3, mine is only en10 as I have tested a number of mobile devices and my mac is a bit of a mess as a result!)
Select the option to open Network Preferences, the new adapter will be displayed:
Click Apply, there is no need to make any changes to the adapter settings.
On the Android PDA launch the PdaNet application:
Select the option to Enable USB Tether.
On the Mac, click on the Menu bar icon and select the option to Connect:
After a few moments the Internet connection will be established, and the Menu bar icon will adjust to include an icon of a globe:
You are now connected to the Internet.