for photos, apparently it HAS to be done in iPhoto, in which you move it's library to the external
for movies, it's simple. Create an alias of your movies folder, and place it into your default "Movies" folder I did it, and when I access front row, I select "Movies" then I Select the folder that shows up "Movies" (i know it says it twice, but the second "Movies" is the folder on the external HDD that the alias points front row to)
I can then see all my movies, access all sub folders (trilogies are all in subfolders together). I also made aliases to my other movie files like "TV Shows".
Music is good 'cause I use iTunes, DVD Player is alright, my "Movies" works. I just need to work on the iPhoto stuff because I really don't like that program.