Make sure you only copy the preset files (.xmp) into the 'settings' folder, specified above, as folders are not supported in Camera Raw. To access the Library location on Mac's running Lion or Mountain Lion (Library is hidden by default). To show Library, hold down the option key while selecting “Go” in the Mac Finder menu on your desktop.
If your still having troubles finding the 'Settings' folder, you can also save a file within ACR and search for it on your computer. When found make a shortcut to the 'Settings' folder either in your side bar or as a desktop shortcut for easy access.
Here is a step by step tutorial on how to make the file to find the 'Settings' folder for where you should put your ACR presets in Photoshop CS6 1. open a RAW image in Photoshop Camera Raw window. (Right click on Raw or DNG file and select open in Photoshop. 2. click 'save settings' in the pull down menu accessed by clicking the icon far right on the grey bar that says basic underneath the histogram right side panel. 3. The save settings dialog opens click 'save', it will now show you the settings folder where you should put all your ACR presets into. You can save your file here, then search for the filename you saved it as in your finder/explorer or spotlight to find the folder, then drag the folder to your favorites or make a desktop shortcut on your sidebar for future easy access.
Here is a link to this tutorial with pictures on our facebook page: Installing ACR presets in Adobe Camera Raw.