Anything you edit in iMovie can be opened in iDVD, which will do all the necessary compression and encoding. In addition to porting to iDVD, iMovie can export in several different containers (MOV, AVI, MP4, DV Stream, FLC, 3G), using many different codecs (H.264, Cinepak, DV, DVCPRO, Photo-JPEG, AIC, CineForm, plus uncompressed 4:2:2, etc). However, MPEG-2 encoder is NOT included in iMovie. iDVD does have it, but only for encoding into MPEG2 directly from iDVD. Mind you, iDVD has recently been discontinued anyway (if you buty iLife, iDVD will no longer come with it). If you do have it, it will work for your project. If you need to encode your iMovie video using MPEG-2 codec, you'll likely need something like ffmpegx (a $15 shareware video/audio conversion/transcoding tool). The tool will allow you to choose your container, audio codec, video codec and any other available options and transcode your project into the format of your choice, without 'ruining the quality' of it. Obviously, how good the result comes out will entirely depend on how small you need the resulting file to be. With MPEG2 and 54 minutes, 4GB will translate into around 12Mbps, which is more than enough for a transcoding without preceptible loss of image quality (assuming the MPEG-2 encoder is of decent quality).

Thanks
In ffmpegx, does it allow me to adjust the GB amount? In iDvd it compresses it dramatically and the picture is poor on large screen.
Cheers
R