Ultimately its upto the end user... intel integrated GPUs aside you can force anti-aliasing on/off in the control panel for nVidia and ATI drivers, for nVidia you can even create an application specific profile with FSAA forced... not sure about ATI.
Forcing it on or off usually has no effect on a Blitz3D program. Forcing it on usually does nothing, and I can remember some reports from people who had antialiasing enabled even when they forced it off.
My advice? Just forget about antialiasing, because it's not going to happen. Or if you're completely desperate for it then try rendering the scene to a large texture and scaling it down to the size of the screen. Performance might be a bit dodgy, you'll have to adjust because resolutions are not generally powers of two, and I'm not even sure how good it will look, but it's probably the nearest you're going to get.