Gary,
MIDI needs a lot less space than wave files. The amount depends on how elaborate the arrangement but is usually just a few kB. Wave files need 10MB per minute for stereo CD quality so one song may take 50MB or so. Mono telephone quality needs about half a MB per minute.MIDI can only play MIDI instruments (including your sound card), wave files can be recordings of anything e.g. the track for your next CD.
Real audio is a technique for transmitting audio over the internet. It is a lossy compression technique which takes sound as in a wave file and compresses it to a much smaller size than wave files with some degradation of signal, acceptable under the circumstances. The reduction in size makes it practicable to transmit over the internet. For more details click here.
By the way tell Lance the source code for MIDItext will on its way REAL SOON NOW.
Cheers,
Alan