Quicktime Isn't Working, iMovie won't import MPG

I need help! I'm putting together a project in imovie, and have run into problem. I can't seem to import MPG into iMovie, and when i simply try to view the videos using quicktime, they play for a few seconds and then 'unexpectedly quit'. I've had issues with imovie before, so i'm sad to see it AGAIN not working. I'm working with Mac OS X Lion 10.7.4

If by MPG you are referring to an MPEG-2 video "muxed" with an MPEG-1 audio layer, AC3 or PCM audio, then what gave you the idea the iMovie could edit such content? iMovie can only edit all I-frame MPEG-2 content which has been stored in an MOV file container with the audio converted to AIFF (linear PCM). Such files are normally created during import directly from a camcorder with file import actions bypassing this conversion process. If the files are no longer available on your camcorder, then you must use an alternative app to convert the files to an iMovie edit compatible compression format.

I got the 'idea' because the .MPG files were opening in QuickTime

"Muxed" files contain a single stream of data in which blocks of audio and video data are interspersed to maintain synchronization spatially. QT files contain multiple parallel tracks of audio video data sychronized temporally to an a common clock. To properly edit "muxed" content at the frame level, QT must be able to access corresponding frames of audio and video data. On the other hand, this is not so for playback. Thus, the "muxed" data is considered "playback" compatible when/if the specific compression formats are supported but not "edit" compatible with QT.

Does anyone know why, if the MPEG files aren't supported, they do open in QuickTime and then 'unexpectedly' quit?

MPG can be use as a somewhat generic file container. While "muxed" MPEG-2/AC3, MPEG-2/MP2, MPEG-2-MP3, and MPEG-2/PCM are probably the most common compression formats found in MPG (MPEG, TS, or VOB) file containers, it can also be used to encapsulate AVCHD H.264 video which is not natively supported by QT. QT 10.1 should normally be a able to handle the "muxed" MPEG-2 content in MPG, MPEG, or TS file containers but not VOB file containers. Since there appears to be a number QT problems associated with the recent OS 10.7.4 update, I have yet to update my OS 10.7.3 software and am waiting to see if Apple gets around to fixing these problems. Your playback problem may or may not be associated with this update since my MPG files continue to play correctly under OS 10.7.3 or it could be associated with an attempt to play AVCHD content (which may begin to play and then lock up the player depending on the file container).

The QT 7 player requires a separately purchased MPEG-2 Playback component to handle either "muxed" or elementary MPEG-2 data. Further, this component only supports the video content and does not support any audio compression formats. Thus, if the MPG file contains an unsupported audio compression format, the QT 7 player will not play the audio. If you don't have the required codec installed, the files will not open at all. QT 7 with this codec installed should play "muxed" or elementary stream MPEG-2 content in MPEG, MPG, or VOB but not TS file containers