Pictures: Upload them to Imageshack: http://imageshack.us/
If you uplaod pics here they take up server space n' stuff.
Then take the direct link to image and shove it between:
If the image is not the right format save it as a .PNG in preview.
Movies: Upload to https://www.youtube.com
if you dont have an account there, get one.
Or if the movie file is large/past 10 mins uplaod it to http://www.SaveFile.com
Files: Simply uplaod your file to http://www.SaveFile.com
Then post the provided link. Only .zip files are accepted.