My friend gave me an avi file (created in AVS Video Editor) for me to synch the sound on, but I cannot get it to play in Premiere CS4. In Windows Media Player it plays the video but not sound, and in Premiere it plays neither. Do I need to download a codec or something? Please advise.
audio codec 0x0055 MPEG-1 Layer 3
44100Hz 256 kb/s tot, Stereo
video codec H264
name H.264/MPEG-4 AVC
Convert to MS DV AVI type2 before importing and accept the quality hit. Your friend should have known better than to give you this material that is only intended for watching, not for editing. Use Google to find a suitable converter.
Along with Harm's suggestion, this ARTICLE will give you more background on AVI (and MPEG, MOV, WMV, etc.) wrappers, and how to always be able to "peek" inside those wrappers to see what exactly is inside.
For adjusting sync, if you are having any issues, this ARTICLE might be useful too.