Flooring Tile - shower tiling question

I'm converting a tub to a tub/shower. Now there is painted sheetrock which I plan to remove and replace with cement board.
There is also a window in this soon-to-be shower area.
I have a couple questions.

1. I thought about removing all the wood trim and sills and tiling into the sills. Does the cement board need to placed in the sill or can tile be placed directly on to the framing around the window?

2. Since this is part of a complete bathroom renovation, I plan to replace the drywall in the rest of the room as well. Is it ok if the cement board extends past the tile where it will be painted/textured, or should it stop at the edge of the tile where regular drywall will then be placed? Knowing that I can paint/finish cement board would make installing it a lot easier especially if the tile doesn't go all the way to the ceiling.

Hi Jst,

You can finish cement board with regular drywall joint compound.

You cannot tile directly to the wood framing. You must install the backer board on the inside of the window opening. I would also recommend that you water proof the backer board in the window sill area.

Thanks for the reply,
How should the backerboard be waterproofed?

Laticrete sells a small kit. Floor and Wall Watertight, I think it is. About $50. It's the most economical thing you can use.

http://www.laticrete.com

It's sold at Lowes here in Houston. Don't know about the rest of the country.