I have replaced all my tabs by spaces in my PHP code source (and I configured Eclipse to use 4 spaces as tabs). When I hit tab, I get 4 spaces, that\'s OK.
So... I also need that feature. Before a began to use Eclipse, I was a Vim user. Actually a still use it for some edit task. There is a vimplugin for eclipse, so you can use it as your Eclipse editor. But its a matter of taste.
You can configure vim to do exactly that: Tab insert 4 spaces. Backspaces deletes indentations.
Here the config for your settings:
set tabstop=8 " This is the default in any editor, Tabs are 8spaces Wide"
set expandtab " Tabs are converted to spaces"
set softtabstop=4 " Tabs are 4 spaces"
set shiftwidth=4 " Indent is 4 spaces"
" Here the magic"
set backspace=indent,eol,start " Deletes over indent, line breaks, edit starts"
HTH