Use the official launcher to download and start once Minecraft 1.7.5.
Go to the minecraft base folder (the official launchers shows it when you click “Edit Profile” as “Game Directory”)
Go in subfolder “Versions”
Rename the folder “1.7.5″ to “1.7.5_extra”
Go in the subfolder “1.7.5_extra”
Rename “1.7.5.jar” to “1.7.5_extra.jar”
Rename “1.7.5.json” to “1.7.5_extra.json”
Open the file “1.7.5_extra.json” with a text editor and replace “id”:”1.7.5″ with”id”:”1.7.5_extra” and save the file
Copy the files from the Xray Mod zip file in “1.7.5_extra.jar” as usual and remove the META-INF folder from “1.7.5_extra”.
Start the official launcher
Click “Edit Profile”
Select “Use version:” -> “release 1.7.5_extra”
Click “Save Profile”
Click “Play” or “Login” to start the game. If only “Play Offline” is available, then log out and log in again to fix it.