Why not simply have it as an option? Perhaps ask the user first time the game is run.
Because when we're talking about users who don't know how many hard drives they have, we could well be talking about users who don't know whether they have an LCD monitor or not. They buy a PC from Dell, HP, Compaq, etc and really don't know much more than that, in many cases.
I doubt there's any way of detecting this. The GFX card has output only, and that's it... unless I'm wrong. :)
Well yeah, the monitor doesn't have output, but they often have drivers ( though I don't intend to rely on this as many people won't have installed them ) so I'm just thinking that they might leave some trace of their existance around somewhere.