Anyway, I usually take dd skins for screen shots, because I don't have to look for them for too long, and I always know they are looking good and are good quality.
Mustang, you're lost cause you've begin on PS, Gimp and PS have almost sames possibilities, off course PS is a lot better, but I think if you use these 2 logs you can make some same pictures.
Paint.Net is quite good, specially if you know what you're doing and install the correct plugins
@TuomasH: You need some antialiasing mate, and how are you bluring the background? I recommend you taking 2 pics, one with the car and one without it, then cut the car from the first one and put it over the second one, so the blur is separed from the car. That should make your pics a lot better :P