For those not using Photoshop, here's another alternative to Paint.NET and/or Gimp: Krita
Haven't checked it out too much, but it seems to support a fair bit more than the other two, e.g. Layer Styles (e.g. Colour overlay), Vector layers. Not sure about Alpha channels, might be in there, as well. Well worth a look, although you'll still have to export to PNG and then open it up in Paint.NET for DDS conversion or the like.
are currently porting their sensibly-priced photo/designer software to Windows, so it's definitely worth keeping an eye on that, too.
Have you ever had a dream that you, um, you had, your, you, you could, you’ll do, you, you wants, you, you could do so, you , you’ll do, you could, you, you want, you want them, to do you so much, you could do anything?