Most any distro that is Debian-derived has the ability to boot over PXE/TFTP/NFS. The client system boots with PXE then the kernel and initrd are loaded over TFTP and executed. Boot parameters (boot=nfs, nfsroot=server:/nfspath) supply the NFS server and path to the distro contents (loopback-mounted ISOs in my setup). The init scripts then mount the NFS export and then mount the squashfs file over NFS as a branch of AUFS or UnionFS. Then this is mounted as / and the boot sequence continues. This is more complicated but much faster then dumping the ISO or squashfs into an oversized initrd and loading the entire file into RAM over TFTP.
Does VectorLinux have similar capability? I didn't see anything in the docs in the ISO.