I just have a few things to add to SupremePain's comments.
Welcome to the forums... you'll soon learn your way around, but the best way to learn where to post stuff is to look at the description for each forum and see which one best fits your comment.
There are a variety of 3d modeling programs, but I believe only 3D Studio Max can actually get models into JKII. There is a free version of 3DS Max called GMax... you can get it on the web.
For skins you should get a good image editing program. I use Adobe Photoshop 7 and Paint Shop Pro, but Photosuite is pretty good too. Many of these programs have demos you can download from the web as well.
For mapping, I find that GtK Radiant is easier to use (and more accessible for beginners) than JK2 Radiant. Both work, so it's up to you, but you can download GtK Radiant from the website
http://www.qeradiant.com). Hope this helps.