A SQL Agent Alert that leverages WMI could run a Job for you. Lookup SQL Agent Alerts and the WMI Event Class __InstanceCreationEvent.

You could also do this a few different ways using an SSIS package that runs continuously watching for files:

Using the WMI Event Watcher Task in SSIS to Process Data Files[/url]

Using the Konesans File Watcher Task in SSIS to Process Data Files[/url]

Using the Script Task in SSIS to Process Data Files When They Arrive[/url]