You can also get a BLP plugin for Paint.net that allows you to save it directly as a .BLP from the paint.net program, rather than saving it, opening a converter and converting it that way.
it doesn't work
i dunno why >o<''
i converted the icons to blp and imported them(BTN&DISBTN) to world editor
but it doesn't show when i use. not even after i reopen the world editor
Ghan has said he has fixed this. Monovertex please confirm this fix. This was only a problem with people that had signatures in the upper levels like not the special members but the respected members.