Please I need help. Server 2008 on vista premium. Is it like an upgrade?

Hello Friends. I've been trying to do dual boot between my vista premium and Xp. But later I discovered I needed server 2003 more than Xp. But since there's server 2008, I thought it would be better if I have a later version. I also saw a tutorial here on ''how to dual boot Vista and Xp, (with Vista installed first)'' Now the problem is that I do not know whether to follow that tutorial for the installation of server 2008 or install server 2008 as an upgrade version on vista. Do I also need to shrink vista volume. Please I expect your kind response. Thanks so much in anticipation. Kaycee