Summarize:

Make sure that the label is facing up when you do this. If any AutoPlay windows open when you do this, close them. Double-click the DVD Decrypter icon, which resembles a CD, on your desktop. If you left the "Open DVD Decrypter" option checked when you installed DVD Decrypter, it may already be open. It's at the top of the DVD Decrypter window. A drop-down menu will appear. This option is at the bottom of the drop-down menu. You'll see a pop-out window appear. It's at the top of the pop-up window. Doing so will set DVD Decrypter to rip the ISO file from your Xbox 360 disc. It's in the middle of the page, to the right of the DVD's name. Doing so will open a destination window. This means that your Xbox 360's game file will save to your computer's desktop. This is in the lower-left side of the window. DVD Decrypter will begin ripping the ISO file from the DVD. Depending on the size of your game, this can take anywhere from a few minutes to an hour or more. Your game's ISO file should now be on your desktop.
Insert the Xbox 360 disc into your computer's DVD drive. Open DVD Decrypter. Click the Mode tab. Select ISO. Click Read. Click the folder icon. Click Desktop, then click OK. Click the green "Play" button. Wait for your game to finish ripping. Click OK when prompted.