Downgrading back to XP

It's final, our family's new DELL 531s is downgrading back to XP. As many people have said, Vista is still unstable until its Service Pack 1 is released. For us, we can't access many websites including Microsoft itself. We've called one of Dell's technicians up here twice, but, the problem still exists. The problem seizes temporarily after reinstalling Vista, but, after rebooting, the issue comes back (Restores Default Settings). Until then, I'll be sticking with XP Home that Dell sent.

CONFIGURATIONS:
Dell 531s
Windows Vista Premium (EN)
2.31 GHz AMD processor
Windows Experience Index: 3.0