If you have an Apple TV 1 (the silver one) and would like to install XBMC on it, then you need to follow the guide below.

Installing XBMC on Apple TV (1st generation)

What you need

• Apple TV 1 (the silver one)
• Mac Computer
• USB Thumb Drive (512 MB minimum) Formatted with FAT32.

Step 1: Get the ATV USB Creator for Mac software onto your Mac computer. Extract the contents of the zip file and open the “atvusb-creator-1.0.b13″ folder.

Step 2: Plug in a USB Thumb Drive (formated in fat32) into your Compute, or format it into fat32.

Step 3: Launch the atvusb-creator.app by double clicking the icon.

Step 4: Leave everything as Default and press the "Create Using ->" Button. It will take a few minutes to create the Patchstick. When it’s finished the word “Complete!” should be on the last line of the log text box.

Step 5: Unplug the power cable from the Apple TV device.

Step 6: Plug the USB Thumb Drive into the back of your device and plug the power cable back in.

Step 7: Wait a few minutes while the Patchstick processes the installation.

Step 8: Unplug the power cable and Remove the USB Thumb Drive from the Apple TV.

Step 9: Replug the power cable back into the Apple TV.

Step 10: Now find the “Downloads” menu under the “Launcher” heading.

Step 11: Click the “Launcher” program to update it.

Step 12: Return to the “Downloads” menu under the “Launcher” heading.

Step 13: Select the latest version of “XBMC” from the options.

Thats it Your first generation Apple TV is now Jailbroken and XBMC has been installed.