Did you load the plugin using mongrel_rails start -S <path to config
where config file is as described in:
http://mongrel.rubyforge.org/docs/upload_progress.html ?
Vish
It's uploading to a temporary directory (Windows/Temp probably, check your TEMP environment variable) and it's available under the controller you post to as a regular Rails TempFile or StringIO variable.
Do something like params[:file].read to get the file contents.
It's up to you to do whatever you want with this file. FileUtils.mv will move it to the location of your choice.
Later, Vish