Wait what
Crown molding goes at the top of a wall hence "crown"...
You use a coping saw for trim,
http://en.wikipedia.org/wiki/Coping_saw
you join corner by scribing them
http://en.wikipedia.org/wiki/Scribing_(joinery)
I wouldnt do crown molding in your house though, it's the wrong style... Moldings are actually part of a unified architectural style. There are specific proportions to wall heights, it's based on classical orders of architecture. The crown molding corresponds to the captial of a column, the field of the wall to the shaft and the bottom to the base.
http://www.buffaloah.com/a/DCTNRY/p/pallad/image/02tuscan.jpg
The crown of that (as an example) is 2:6 the height of the wall. It would look right on a Georgian type house, in say New England. You have a tract house, there are no elements like that because the style is mostly based on the size of the materials used to construct it (4'x8' sheet goods and 8' length studs 16" on center). It would look tacky and makes the ceiling a lot darker.