I am new to linux and very new to linuxmce, so I will not be much help with the integration, but I am fairly familiar with drupal and I think it would be the obvious choice over joomla. Huge community, grreat support, thousands of free modules, etc, etc.
If someone can intergrate this with linuxmce there is already a drupal module that does most of what is requested here. Homebox http://drupal.org/project/homebox
would provide the ui for this. You can add google gadgets (calendar, mail traffic, directions, etc.) or your own data and drag, drop and resize the "boxes". There may be a problem with dragging a "homebox" with a google gadget embedded in it. I have seen 1 issue posted related to this, so it may or may not work. I will look into that. It may be an iframe or java issue. Does anyone know about google gadgets? Are they iframes?
I am wiring my house now to install an mce network and would love to see this added.
Off topic: does anyone know about a 10.04 release? or boxee (or similar) intergration?