My sites always (well usually) have a top masterborder which contains the repeating site navigation and any graphics such as a logo that I want to repeat on every page. I close both left and right masterborders so I'm only working with the layout. I then place a layout region with either an image background or, more ususally, a coloured (white) background and place my content in the layout region. Sometimes I also have a lower masterborder which contains a footer. Make sure you check Centre Layout in Browser in the layout properties before placing the layout region. That's my workflow; you may find other ways of doing what you want.

Re the repeating image. I take it you've tried the background tab in the Manage Styles dialog box to set your image to no-repeat?