You can do it either with Vista or Linux.
All condesed into
Just booting tips.
Either boot loaders can boot 100+ systems if you've got them. Linux is possibly 2 to 3 times easier. In fact if you use Vista to resize the hard disk to obtain an unallocated space in the hard disk first, tell an Linux installer to install itself in the empty space there is a 95% the Linux will do the dual booting "automatically" for you, without lifting a finger.
It is the duty of every Linux installer to scan every partition for a boot loader and include it in the booting menu. Well every Dos to Vista has a boot loader installed in its boot sector or dies so it is almost impossible not to end up with a perfect dual boot system by installing Vista first and Linux second. Still people manage find ways to screw it up.