You drag the tab to where you want it. It's kind of weird, must be a Java thing. Try dragging it toward one of the edges of the open editor window and eventually, in my case at least, a splitter bar will pop up. If you let go of the mouse it will divide it there.
I don't know if that's standard Eclipse since I'm using Altera NIOS II IDE, which is based on Eclipse with the CDT plugin. Where exactly the editor functionality comes from is hard to say but my guess is that it's standard Eclipse editor stuff.
Try Window|Preferences. In the tree view on the left open "General|Editors|Text Editors". In my case there's a list box labeled "Appearance color options" with "Background color" and "Foreground color". Uncheck the "System Default" box and you're good to go.
I'm not a huge fan of Eclipse in general (can you say "hog") but I love the CVS integration. That really makes it fun to work with CVS.
Andrew