Not to sound insulting or anything, but are you looking in the correct directory (in your EQ2 directory as opposed to the directory for the ThorUI AutoUpdater)?
All the UI files (which are kept in the UI subdirectory of your EQ2 directory) are .xml formatted files.
If you are wanting to revert back to the default inventory window (or use a different mod), I believe the file you want to delete/replace is eq2ui_inventory_inventory.xml.
"Certainty of death! Small chance of success! What are we waiting for?!"