There is an Adobe tech-note on this:
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http://kb.adobe.com/selfservice/viewContent.do?externalId=kb 402028>
But there may be a problem in Photohsop locating any presets in the folder using the browse window that you get when you click Load. (at least on Windows Xp).
However if you Browse all the way to "My Computer" and follow the path c:\, Program Files, Adobe, Adobe Photoshop CS3, Presets, Duotones, Duotones, Pantone(R) Duotones it does find the folders and presets; (each of the comma-separated items that I have listed is the sequence that follow by double clicking in successive browse windows!)
(I think that I got it to work as I have described, but cannot replicate the initial problem when I restart Photoshop, so it may work for you the first time.)