If you want "skin tight" clothes, you need to either get a paint program (MS Paint, Paint Shop Pro, Photoshop, Painter Classic, etc.), or just raid the various texture sites and the Free Stuff here. If you want conforming or prop-based clothing, you need to get modelling programs (Nendo, Amorphium, Ray Dream Studio, Carrera, Rhino, Truespace, 3D Studio Max) or loot the various clothing and prop sites and Free Stuff here.