Things You'll Need
Instructions
Open your Web browser and navigate to the Nem's Tools website. Click on "Installer (2,112 KB)" to download the VTFEdit tool and save the executable on your hard disk drive.
Double-click on the "vtfedit133.exe" file you downloaded earlier to start installing the tool. Follow the instructions you see on your screen to finish the installation.
Double-click on the "VTFEdit" icon on your desktop or click on the "VTFEdit" icon in the "Start" menu.
Go to the "File" menu and select the "Import" option. Use the built-in file browser to select your image and click on the "Import" button to open it in VTFEdit.
Use the built-in set of tools to edit the image. This is not mandatory, so if you are satisfied with the image, there is no need to edit it.
Go to the "Tools" menu and select "Save as." Select "VTF" in the "File type" drop-down box and type "background01" in the "File name" text box.
Use the built-in file browser to navigate to the "Program Files\Steam\Steamapps\YourUsername\Garrysmod\Materials\Console" folder.
Click on the "Save" button to save the file to the "Console" folder. Select "Yes" when prompted to overwrite the existing background, then close the VTFEdit tool.
Go to the "Start" menu and click on the "Computer" icon to start the file browser.
Select an MP3 file, right-click on it and select "Copy" from the resulting menu.
Go to the "Program Files\Steam\Steamapps\YourUsername\Garrysmod\Sound\UI" folder, right-click anywhere on the blank space and select "Paste" from the resulting menu.
Right-click on the MP3 file and select "Rename" from the resulting menu. Type "gamestartup01" as the file name and press "Enter" to rename the file. Your MP3 file will play every time you start the GMod server or change the map.