Well, I thought I'd just wait until Squarespace 6 came out before I would be able to successfully add a full screen background... but, during a search for adding "responsive" code, I found this wonderful resource: Squaretuts.com. Cool, adding the code was a snap. How awesome.
Now, my home page has this cool, kinda 70's vibe background. I checked it using Adobe's Browserlab and it works A-OK.
BUT... I'm still messing with the HTML5 code so smart phones and tablets "respond" by shrinking each page. Squarespace 6 is doing the responsive thing automatically, which I just LOVE... but I need it right now. I'll need to learn it this weekend, I guess.
And as I write the code to redesign my website to be responsive, I'm starting to think I want my website to look the way I want it to look on all different devices... and maybe an automatic responsive code may not work for custom websites... but will be perfect for templates.
More on this later...