To expand on akira's tip above on using Lubos Lunak's "fake xinerama", here's exactly how I made it work for me:
- I downloaded this Xinerama.c file from the Fake Xinerama site.
- I opened a terminal, and navigated to the folder folder where I saved Xinerama.c.
- I executed:
gcc -O2 -Wall Xinerama.c -fPIC -o libXinerama.so.1.0.0 -shared
- I opened up nautilus (the gnome file explorer) as root, by typing Alt-F2 and then:
gksu nautilus
- I navigated to /usr/lib, found libXinerama.so.1.0.0 and made a back up copy of it.
- I copied the libXinerama.so.1.0.0 from my download directory into the /usr/lib directory, overriding the copy there (which I had just backed up in step 5, so I could undo this later if need be.) To keep things clear it was helpful to note that the file size of the "fake" version was bigger (12.6 kb) than the "real" version I was replacing (8.6 kb).
- I created a new text file called .fakexinerama in my /home/dave directory and put this in it: (based on my 1440x900 physical screen size)
2
0 0 720 900
720 0 720 900
Fake Xinerama lets you define any kind of virtual screen set up you want, but I just want a vertical split screen. To achieve that on your monitor, X by Y pixels in size, looking at my file example, just replace 720 with X/2 and replace 900 with Y.
That's it. I logged out and back in, and was up and running.
Thanks again to Lubos Lunak for creating this mod and to akira for pointing me at it.