If you have the .ecc file, you should be able to just plug in the USB drive, open it and copy the file into the 1st window.

If you're having problems with the extraction process, what extension is on the file before extraction? Even if it's an .exe file it may be a self-extracting zip file that can be opened with an app like Stuffit Expander.

http://www.stuffit.com/mac/expander.html