So long as your texture for the Dress didn't use anyone else's work, you're free to give the texture away or sell it as you please. As for texturing, it's like odeathoflife says, grab the template and start painting. Every so often, save your work and load it into Poser to see how it is coming along. You'll also need to make MAT files to load your texture onto the Dress if you want to sell it. (I can't think of a store now-a-days that won't expect a MAT file for each texture.) Cheers!