MPEG is a distinct file type and compression type. There is mpeg-1, the oldest type, mpeg-2, the type used with most DVDs, and mpeg-4, the newest type of mpeg compression that Apple includes in QT 6. The latter is the only kind of mpeg compression QT Player Pro can do without added software.
There are several third-party compressors that run on the Mac. First, Toast Titanium, the CD burning software by Roxio will do mpeg-1 (version 5) and also mpeg-2 in the new Toast 6, to be released this month. Movie2MPEG, which should work in Classic, is a freeware encoder. It is kind of tempremental and I don't really recommend it. ffMpegX for OS X (10.2 and up I believe) will do both mpeg-1 and mpeg-2.