You can easily position a window in the center of the screen if you want:
// Centering the window
dw = desktop width() : dh = desktop height()
width = 800 : height = 600
xpos = (dw - width) * .5 : ypos = (dh - height) * .5
set window on
set window size width, height
set window position xpos, ypos
sync on : sync rate 60
set text size 36
text 200,200,"How's this?"
text 200,240,"Spacebar to exit"
until spacekey() = 1
This assumes, of course, that your desktop screen is larger than 800 X 600.
So many games to code.....so little time.