Well, you can get the JK2Radiant editing tools, which comes complete with Modview.exe, for actually viewing models. This is helpful if you are skinning a model (I know, because I've used it recently myself).
As for actual programs to make the skins...I use paintshop pro 7. It works for me. You can do masking/layering with it, which you may need to apply to the UV skin maps. Open up some of the skin files in the assets.pk3 to see how the skins are laid out.