The Sims 2

Music: In order to play your own music in the game, just go to My Documents\EA Games\The Sims 2\Music, and drop your .wav or .mp3 files in the appropriate folder.
TV channels: To have your own movies played on the in-game TV channels, just go to My Documents\EA Games\The Sims 2\Movies\ and place .avi files in the appropriate folder. Ideally, the files should have stereo sound, and be in a 128x128 pixel format, otherwise they will be stretched to fit.

Video games: In order to have your own files played as video games, take any existing .avi file that you have. Then browse to one of the game subfolders under My Documents\EA Games\The Sims 2\Movies\Games\ and place your files in the appropriate folder. Rename your movie as the exact name of one of the existing movie files (gamename_ATTRACT.avi, gamename_INTRO.avi, gamename_P1LOSE.avi, P1WIN.avi, gamename_P2LOSE.avi, or gamename_P2WIN.avi, where gamename=bus, ssx, or sc4). Then when you play the corresponding game segment in The Sims 2, your movie(s) will play on the screen instead.