GPG4USB doesn't have to be run off a USB, it's just an installer-less program that can be extracted anywhere, including your hard drive. The reason why you should use GPG4USB is because it's less buggy and easier to use than GPG4Win. Here's a good example, start with this comment, where BlarghRawr wanted to verify a signature of mine with GPG4Win. http://dkn255hz262ypmii.onion/index.php?topic=95761.msg684493#msg684493 The conversation continues over a few pages, but he failed with that program and succeeded with GPG4USB.