Scott pointed me in the right direction as to my problems in getting .Text moved to a subdirectory.  Turns out there are a different set of HttpHandlers required which can be found in Single2_Web.config.  Now, both .Text and nGallery are happily coexisting at Casa dé Hambone.

As for why I was having a problem with .Text in the first place, it has to do with how ASP.NET’s inheritance of Web.config works.  In this instance, the parent’s HttpHandlers are processed before the child has a chance to clear them, and therefore the parent’s handlers try to run from the child web.  The recommended workaround is to place the assemblies containing the handlers in the Global Assembly Cache.  However, I’m not real comfortable with that solution and have chosen instead to move my blog to http://www.casadehambone.com/blog, effectively removing it from the root and eliminating the problem.