The TwinView info is on http://us.download.nvidia.com/XFree8...ppendix-g.html
Yes, Twinview is used to fool the X Server into thinking you have one display.
XFree86 is a less-well supported X-server. X.Org forked from XFree86 due to various disagreements over the license that it was released under. Most people now seem to be using X.org - there is actually a bit of info on this on the x.org website, if you are interested.