In what way did the machine hang?
Did you use different filenames for the second db?
Is the second db running or not? I'm not sure about online backups in 8.3.
What size are the db's you want to backup, and how much disk space do you have in the backup target location?
What block size are each db? A different block size setting on the db changes the amount of space a -vs file uses.
Using the -vs param is an interactive command line program. It will prompt you for the next filename once it fills the first file to the specified size. If you tried to run from at, cron, or in the background without providing redirected input, it will hang waiting for you to provide filenames.
We need more info to help you. Saying something doesn't work doesn't give us a lot of clues.
Hope that helps.