Go to the root folder of whatever emulator you're using and find a folder labeled 'plugin' (if there isn't one, create one and put all of your plugins in it). Then, create a folder called 'hires_texture', this is where all of your texture packs will go. Finally, create yet another folder within the hires_texture folder that has the same name as the ROM header of the game for which you want to load textures (the ROM header is what shows up on the top of the window when playing something on PJ64, for example); i.e. Ocarina of Time would need a folder named 'The Legend of Zelda', Majora's Mask's folder would be 'Zelda Majora's Mask', etc. Within each of these game folders is where the actual texture packs will go. Just be sure to move the texture packs out of the game folder when they're not in use; you can move them out to the hires_texture folder if you like (that's what I do).