I usually encode to SVCD using DVDx, so I don't know if this really applies. each encoding format has its own "default" settings or whatever, which means that in burning to CD the amount of data isn't ness the amount of data you see on your hard disk.
what program you using to burn? they normally have some indication as to how much space you have left on your media.
What exactly do you want to burn? mpeg files onto VCD? or are you ripping a DVD to burn onto VCD?
Like I said, difficult to say, but if you're burning onto VCD, nero or whatever should tell you when you're running out of space? you could always just play it safe and burn to a 74 min Cd / 650 mb of data and leave the rest as a buffer...
best way to figure out biterate is use a bite rate calculator but for basic vcd I wouldnt worry about it it will still go on 2 disks sometimes one best bet is to make svcd and set the biterate exactly so you can make it fit on 2 or 3 disks for better quality check out vcdhelp.com and down load there biterate calculator its java based html just add in the time of the file your trying to convert like with me I add in the time of the dvd I rip say 93 minutes etc.. and biterate calculator will tell you the data rate to fit it on such in such ammount of cds say 2 or 3 most movies Ill do 3 disks