VCD/SVCD's can be burnt in 2 ways:
Data:
Has the same constraints as a regular cd. 700 megs and you're finished.
VCD:
In this option w/ programs like Nero, the movie is acually recorded just as sound is recorded so you're costrained to 80 minutes of movie per cd just as audio would be. This is the way you burn a VCD if you would like it to play on a capable DVD player.
Data and audio are both recorded differently on CD's(which is why you can put more then 700 meg of "raw" data on a CD when the file is a VCD/SVCD. I don't have time to go into the indept detail of how both formats are recorded on a CD and why they differ in constraints, maybe this is where someone else can pick up my slack
