Download the zipped executable from here, run the installer, and look for the "Compute distance to Panels" tool in Add-Ins>External Tools. There are some sample files to try out in the package as well. By default they are installed to C:\Program Files\Revit buildz extensions 2010\samples.
Summary of the last post: the plugin calculates the distance between curtain panel by pattern instances and some other placed family, then writes this number to an instance parameter in each panel. The download includes a readme file with more instructions, but you can also read more in the original post.