ok, with ssis you are going to have to have some sort of monitor that fires an event which could then execute the ssis package.
This is really not what SSIS is designed for.
What you really need to do is create a windows service. In this service I would recommend you implement the FileSystemWatcher on the folder you want to monitor. Using the events that get fired when something changes, you can then execute a proc directly. If however you need the processing within the SSIS package then just execute the package passing in the fileinfo details.
some references below:
Creating a simple Windows Service[
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http://blogs.msdn.com/b/michen/archive/2007/03/22/running-ssis-package-programmatically.aspx[
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