Please see the most recent updates in the "Where did the .com name go?" thread. Posts number 16 and 17.
The only FsX native Apaches that I know of are the Virtavia models. I have the 'D' model and it looks and flies good, but there's no systems modelling at all. (And they botched the roundels on the Dutch version....)
Edit: There's the Area 51 Longbow as well: http://www.area51sim.com/apache.html