I'm trying to scale my window, for example from 440*420 to 320*240.
How can I easily do this?
It's been a while since I last used SDL 1.2, but from what I remember there are two options.
First, SDL by default works in software mode. If you're not using OpenGL, then you'd have to grab the screen buffer SDL_Surface and scale it to your window's size (probably SDL_Image has a function to do that).
Second option is if you're using OpenGL. After resizing the window, you have to change the projection matrix, and the viewport. Projection matrix defines how much the user sees, viewport scales it to the window. If you set matrix as if the window is 320x240, and set the viewport to 440*420 (window size), your rendered scene will be warped to match the window/viewport.