AirDrop is one of the great new features of Lion that provides a really easy way to share files between supported, Wi-Fi enabled Macs, without having to connect through the local Wi-Fi network. AirDrop is a breeze to use if you have the right Mac.
You’re out of luck if your computer doesn’t have the right hardware—specifically, if it doesn’t have Wi-Fi chips capable of personal area networking (PAN) for peer-to-peer connections. Many Macs, even many of relatively recent vintage and many that can run Lion, don’t have those chips and so can’t use AirDrop. (Apple provides a list of AirDrop-capable Macs here.)
But, it turns out, there’s a workaround. If you have one of those older Macs, you can add a setting to AirDrop’s defaults that allows AirDrop to work over regular networks, not just PANs.
The change is a one-liner: Open Terminal and, at the command line, type:
defaults write com.apple.NetworkBrowser BrowseAllInterfaces 1
Hit Return, then go back to your Desktop and hold down the Option key as you Control-click (or right-click) on the Finder icon in the Dock. Select Relaunch from the contextual menu; relaunching the Finder activates the code you entered above. When the Finder finishes its restart, you should see an AirDrop entry in the Finder sidebar that wasn’t there before. (You can reverse the process by using the same command with 0 instead of 1, and relaunching the Finder again.)