It would help if you provided a bit more information.
What version of Vector Linux have you installed? Also, how did you install Grub, since its not normally part of the Vector install (Vector uses Lilo by default).
By the sound of it, you need to add the correct entry to /boot/grub/menu.lst, but you will need to be booted to Vector to do that. For general information, this is the menu.lst entry I use to boot Vector 5.9 Standard:
title Vector Linux 5.9
kernel (hd0,8)/boot/vmlinuz-22.214.171.124 root=/dev/hda9 vga=791 splash=silent ro
You would need to change the hard drive entires to suit your drive layout, and possibly adjust the "vga=" entry to suit your display, but otherwise, the entry should be pretty much as above. Of course, you need root access to edit /boot/grub/menu.lst.