Actually, I'm not sure if I figured out how to make the movement keys treat spaces as tabs, I guess I normally end up using 0/b/$/^ if I need to navigate around them (sorry!). These settings are what I use, and will at least change backspace to delete 4 spaces in one keystroke instead of 4, which is what always annoyed me most.

    set tabstop=4
    set shiftwidth=4
    set softtabstop=4
    set expandtab