Let me give you some links to interesting pages.
An absolutely fantastic collection of resources for clothes designers is at Haute Couture. Do check it out, it rocks !!!!
Here is a tutorial on how to build a photostudio.
Here you can learn how to build and how to make your own clothes with Photoshop or The Gimp
Here you can download photoshop files to make your own skins (they can be used with TheGimp too)
Here are more files for free skins from szemra.