Windows Vista upgrade options?

I am based in the UK, and I see that most of the laptops on sale in the
retail market are still at best Windows XP Professional version, if not
Windows XP Home Edition.

Can I ask, for a non-commercial, retail laptop
- what is the upgrade/licensing option to go from Windows XP Home
Edition(OEM) to Windows Vista Ultimate?
- what is the upgrade/licensing option to go from Windows XP Professional
Edition(OEM) to Windows Vista Ultimate?
- what is the upgrade/licensing option to go from Windows Vista Home
Edition(OEM) to Windows Vista Ultimate?
- what is the upgrade/licensing option to go from Windows Vista Home Premium
Edition(OEM) to Windows Vista Ultimate?

Sorry guys, realised I should be posting to the Windows.Vista.General
newsgroup instead for this question!