nm delete thread...
you're booting an ubuntu livecd, and trying to format your disk?
If so, you'd need to unmount /dev/hd<whatever> or /dev/sd<whatever>, and it will no longer be busy.
If you're trying to format the drive you're currently booted to, that won't really work... so get a livecd.
EDIT: well, you could sorta make it work in certain instances, but I'm not addressing those.