Hoo, such a comp sure sounds like a lot of work .. Some of these bands are known for putting out some real epics (close to the edge, tarkus, nine feet underground, thick as a brick etc.) and since it's a compilation of prog bands, it would make sense to include those. If you do include those, such a compilation will grow to a size of gigabytes very quickly.
My guess would be at least 3 gigabytes of music for 100 tracks. Megaupload I think can handle up to 1 gig per upload, so then you could split it in three f.ex.
I could help with the comp though if someone wants to have a go. Not with hosting, but providing songs.
