Vista - Upgrade Question

I've got Vista home premium upgrade and XP Pro. I haven't tried very hard
but I can only start setup from within XP. I'd like to do a clean
install.I've had it installed already, and even
though I choose not to save my old XP stuff it does it anyway. Then when I
try to access or even delete files that are left over from XP, I get the
access denied thing, which makes sense since
XP Pro encrypts everything. But it's annoying too.

Ideally I would like to install Vista on my other PC rather than have them
dual boot. But I've already activated it on this one. Is there a work around
for that or am I stuck using it on only
this PC? I've had some major issues with Vista, and I'm starting to think
Vista is nothing more than another Millenium.

I have 4 other versions of XP, all legit, 1 other Pro and 3 home. Can I
upgrade a home version?