useradd ftpuser -d /homedir
passwd ftpuser

Changing password for user <username>
New UNIX password:
Retype new UNIX password:
passwd: all authentication tokens updated successfully.

vi /etc/passwd
ftpuser:x:506:508::/homedir:/sbin/nologin

vi /etc/vsftpd/vsftpd.conf
chroot_list_enable=YES
(default follows)
chroot_list_file=/etc/vsftpd.chroot_list

vi /etc/vsftpd.chroot_list
ftpuser

/etc/init.d/vsftpd restart