You must be on a Mac. By default the Application Frame is on. Turn it off.
Right I am on a Mac. Yes, turning that Application frame off allows me to do this, but where's the background pallete that was in CS3? It's just my normal desktop right? Kinda weird, but OK.
What I did was change my space to have a solid background and that's a bit better, but if you turn off the application frame and load a second file, the first goes away anyway, unless you change the Windows->Arrange to "Float all in Window". This isn't a "permanent" setting so you have to set that EVERY time you load a new image. That's pretty poor functionality. You can't even save the workspace that way. This is a pretty bad nuisance.
Not sure what you are calling background pallet. But the toolbar with BR and suff was eliminated in CS6.
On a Mac, Curt, OSX allows you to have multiple wokspaces (usually called virtual desktops in the Windows world). Each virtual space can have it's own background. When you turn the Application Frame off, all you have on the screen is the tool pallete and any windows at the far right and the menu bar at the top, until you load an image. So it just loads over your base desktop background. I changed this to a dark grey background so it's a bit nicer to use as a backdrop.
But it still doesn't solve the problem that when you load a second image the first goes away until you "arrange" them by floating or tiling. That's my point.
Hello, the application frame is just a background that isolates other Applications from Photoshop's interface.
It wasn't there in previous versions, but it does not interfere with the tabbing of documents.
What you need to do if you do not want the tabbed documents behavior, is to go to photoshop>preferences>interface, and uncheck "open documents as tabs" and "enable floating documents windows docking"