How to install full version of vista with XP installed

My dad's friend helped me build my computer but when I got it back, it had windows XP sp3 installed. I have a windows vista home prem SP1-bit OEM DvD and when I insert the DvD and restart the computer nothing happens.

Can someone help me install vista plz

What do you mean nothing happens? Do you mean it boots back into windows? You need to go into your bios and make sure your dvd drive is set as the first boot device.Captain__Tripps

It just goes to windows xp, and if you could give step by step instructions that would be helpful, ty.

When you turn your computer on, enter into the bios. Find the boot settings. Change the first boot device to cdrom.muirplayer