Well, if you don't own them, then you're going to have to find a way to get access to them. All you need is access to each of their .GCF files. So perhaps if you have them "preloaded" for free, then their .GCF files are already there, you just need that free program GCFscape in order to open them. Once you have those open, you have access to whatever is in there, and the folder structure is just like that of the ones you already have in Windows. like under half-life 2/hl2/materials/skybox/ and so on.

Just make sure to give credit where credit is due....