I've been asked this question many times since Aperture 3 shipped and I published my black & white presets, so I thought I'd write a quick blog post with instructions to have somewhere to point people. It's a really simple process that takes only a few minutes once you know what to do. Here's how I do it:
Step 1: Open the Edit Presets Window
To access the presets menu you need to have the Adjustments tab selected. Click on the Presets button, then Edit Presets... at the bottom of the drop down menu. This will open up the Edit Presets window where you can manage your presets.
This is an important window as it'll allow you to organise your presets into folders, rename them (both folders and the actual presets), delete them, and even view which adjustments each one is made up. In the image above you can see on the right column what adjustments my B&W Preserve Shadows preset is made of.
Believe me, this window will be your friend once you start accumulating a serious number of presets. It's easy to get carried away and end up with way too many of them and completely disorganised.
Step 2: Install the preset
From the Edit Presets window, click on the gearbox icon in the lower left. A new menu will appear with a few options. Click on Import, find the preset you want to install and click OK.
That's it. Your new preset(s) is(are) now installed and ready to use.
By the way, if you want to Export your own presets to share with others, just click on Export from this same window.