first thing you want to do on most or all texture skins is convert the dtx into a psd or xcf, depending on what your using gimp or ps, that being as when you cut and paste images you have the ability to paste it on a new layer so that you can adjust where the pasted images is located before you merge the layers together for the final build. also about the size matter try to work with the size ratio on the image you are going to cut and paste on to the texture on the same magnification ratio, so say your working at 66.7% magnification on the texture, work with the same mag on the image so that when you copy and paste it will be relative in size.
happy skinning Aec