Assuming you are planning on mitering the corners, the same methods are used whether a power miterbox or by hand materbox. Assuming your corners are 'actually' 90 degrees, here's what you do. Crown molding goes into the miterbox 180 degrees off the way it's mounted. This means the piece is put into the miterbox, bottom side up. You orient it to the fence the same as it would be on the wall. If the top edge would be 1" from the wall when mounted, it's 1" from the fence when you're cutting it. You may want to make a auxilry fence to hold it in place. Once you have it in place - cut it. If your corners aren't 90 degrees, then adjust your cut accordingly.
If you want to cope your corners, one piece goes up as normal with no corner cuts. Other is cut as noted. Once cut, cope the edge of the cut to the profile of the crown molding. It should overlay the first piece on the wall.

Hope that helps.

[This message has been edited by hcbph (edited January 27, 2004).]

Alter Eagle Construction & Design

go to owners notebook / tutorials

or put "how to install crown molding" into any seach engine and it should come up.