Google your PC monitor model number, and see what its max Screen Resolution is. Mine is a 20" which is 1280 x 1024
Set your PC screen resolution to that size.
You can run Trainz windowed, by editing out -fullscreen and instead typing in -windowed into the Trainzoptions file. Then set Trainz Display Resolution to run the next size down from the PC screen resolution, in the Options page in Trainz. Which is 1280 x 960.
Now I can chat on Yahoo, look at topo maps and Google Earth Images, all the while laying track in Surveyor...by sliding the Trainz screen half way off to the side.