i was watching a video tutorial by Hydropix and he is able to go into a folder he created of photos of textures and ornate doors and stuff and bring that image onto the one he was already working on. It also seemed like he could bring that picture in without it being in its own window like what would happen if i did File --> Open. With that imported image, he could then change its opacity and reshape it. Does anyone know how to do this?

Also he goes into an option where he is changing certain colors of the wall and floor; does anyone know what option that is?

This would be of great help... and if you wanna watch the video to see what im talking about here it is.... http://www.hydropix.com/tutorial.htm