Does anyone have any links to guides on using the Sites in Category webpart?

I'm trying to use it as a rollup of sites in a certain category on a
page in my portal. It works in the out-of-the-box Sites directory
fine, but I'm trying to put a version of the webpart on a page that
will list all sites of a certain category. When I do I just get "There
are no items to show in this view."

I'm guessing I need to edit something in the Parameters Editor, but
I'm not sure what yet. This looks like a start:

<ParameterBinding Name="sdwp_filterfield" Location="QueryString[Column]"/>
<ParameterBinding Name="sdwp_filtervalue" Location="QueryString[Value]"/>

I know the values, I just don't know how to hard code it instead of
asking for it from the query string.