Another powerful editor IMHO is Greenfish Icon Editor Pro
. It can also easily convert alpha PNGs to alpha BMPs, convert PNGs, BMPs, GIFs with no alpha transparency into such with alpha transpareny saving them to one of the above formats + ICO . As a matter of course you can also resize (stretch/crop) your images and some nice filters are also included.
GFIE Pro is freeware, requires no installation and leaves no traces in your Windows registry.
magic pink 2 alpha: