Of course, if you realize that very soon after rendering starts, you can cancel the render, fix it, and start rendering over again. You won't lose much time at all, especially compared to being unproductive during the whole render cycle.
I'm running with 2 19" flat panels and I can't see any benefit to using the external monitor setting. What am I missing? I can preview just about any size video I'm working on (save 1440 width) just using the normal preview window which I can move around or minimize even whilst rendering.
Alt-Shift-4 is the keyboard shortcut to toggle external preview. I've pasted this on my second monitor, 'cause it's not an easy one to remember, and most of the time my primary monitor goes black when I switch to external monitor on secondary windows monitor (making it very difficult to find the icon, or look up the shortcut in Help!)
i use a matrox parhelia and a g400, to run 3 monitors, including my dell widescreen, and 2 plantronics 21" on each side, works terrific, on my win2k system..