How come after I have downloaded visual site designer and the photo gallery, the photo gallery when I click to use it in visual site designer, I'm asked if I want to download it again, I want to add a slideshow to the current project I am working on.

There may be a simple answer to this, so thanks for reading and anyone who can answer this question.

There is a very simple answer. Just go to the Settings Menu > Configure Left toolbar and update the installation path for these programs.