There is no software specifically for this purpose with pre-loaded templates. If you want to create designs for Skins professionally, it's best to invest in Photoshop. We may have other plans for normal consumers but we are not able to reveal them just yet.
Our templates are available for free at
iStyles Support Center but the newer models are password protected for internal usage only, for competitive reasons, as they were copied by competitors in the past when they were all freely available.