Trim removal question: How to make my interior seamless -- Lotsa Pictures
 

All windows, doorways, and wall corners have crappy wooden trim borders:

http://plaskon.netfirms.com/images/diy/corner.jpg

When I take the trim off, there is a gap between the dry wall and the sash.

http://plaskon.netfirms.com/images/diy/gap.jpg

What can I use to fill the gap?
And how can I ensure that the gaps between wall corners maintains a sharp edge like this?

http://plaskon.netfirms.com/images/diy/seamless.jpg

I'd appreciate your suggestions.

Umm,, I see no pictures.

Gently push insulation into the gap. Just fill it loosely, no cramming. Some people will use expanding foam. I have seen expanding foam swell until the jamb is too tight to let the window sash move.

When I trim a window, I put the side casings on first with only a loose nail on the bottom on each side. I set the top piece on top of the side casings and then I can adjust the sides and the top to fit, or I can see the problem before I've nailed anything permanent.

Is that what you were asking?

I pulled up your pictures,
 

Not so bad, not great, seen worse.

You need shims between the hinges and the framing. Then shims between the latch strike plate and the frame. Then near the corners on the latch side.

woodfiller and/or caulking. Clear painters caulking between paint and stain works well if the cracks aren't too big.