textures

Hi!!
I have some questions about textures for PSP8 which I cannot found in the memories:

1. Where can I download some textures??
2. What kind of file are the textures?? Are they all GIF or JPEG or something else?? If it's something else then GIF or JPEG, do I need to download a special programm?
3. How do I import the textures into PSP8??

Thanks for the help!!