Check this out: MyTrigger

My friend Erik has not yet
mentioned this on his blog, but I
feel I need to tell the world about his latest project, MyTrigger. Basically, it’s a small app that lives in your system tray and waits for various system events (WLAN changes, USB device insertions, processes starting), and then executes programs or scripts in response.

For example, you can use it to mount/unmount network shares whenever you entter or exit a WLAN, start your webcam software whenever you plug in your USB webcam, or bring up a notification whenever a background process starts.

After having the 1.0 version for a week, he has now brought forth
1.1, which adds triggering on file system changes, such as when a file
changes or a file is removed from a directory. This stuff can be used
as electronic duct tape for a lot of scenarios.