I just updated include_HTML to version 0.3.  This is basically a bug-fix release; it turned out that the solution I worked out to resolve compatibility issues with WordPress 2.7 was causing problems when trying to access URLs containing special symbols.  I also added a little extra functionality; now you can include absolute local URLs starting with a forward slash; handy if the inclusion runs on the same server as the including instance of WordPress.  Users are urged to upgrade.