(1) I don't have enough subscribers using Outlook 2007, so I really don't worry too much about it. (My subscribers are not corporate types.) But I do include a link at the top of each message that says - "if you are having trouble seeing the images in this newsletter, please click here to see this message in your browser." That takes care of most rendering issues.
(2) Since the background image allows you to apply text on top of it, you would need to create a new image, with the text already there. Then, you use the image as a normal image (Image button on left hand panel while in edit mode) and remove the background image from the code (using the Global Settings from the left-side panel while in edit mode).
I have a related question. I'm going through the yearly re-design of the various custom templates that I use (about 4), and for one of them I've been using a background image as the header. It's a fairly simple black to white gradient with a curved corner set above a table with a thin border (here's an example). I did this so that, even with images blocked, the header text would still show.
In designing for Outlook 2007, I know background images won't show up. But if I convert the header into an image and someone has images blocked, they won't see anything in the header (minus any specified 'alt' text).
I read an article from MarketingSherpa dated Feb 16, 2007, that stated 59% of email users routinely block email images (including my co-workers, who didn't even realize they were blocking images).
I unfortunately don't have data on how many use Office 2007, so now I'm in a bit of a design quandary.
Has anyone else had this same concern? I've read that background colors will still show up in Outlook 2007, so I'm considering just changing the header background into a solid color. It's not as neat as I'd like it to be, but it may be my only option.