I have installed OpenMRS 2.5 in Windows, I try to add a module, from what I search you must attach the omod file. In windows omod file is simply a folder.
Did you get a chance to look at this? http://www.flossmanuals.net/openmrs-guide/customizing-openmrs-with-plug-in-modules/ By the way, which module are you trying to add?
I’m planning to add and to try the Print module https://github.com/openmrs/openmrs-module-printer