I had installed Windows Vista Business upgrade on an XP professional machine. As you are probably aware, it is the 'upgrade' that requires you to install OVER a previous installation of Windows. Just today I heard about the Windows Vista over Windows Visa trial variation. None the less, I decided to use a 'clean' install of XP to start with.
The windows XP install was done via a Ghost image that I'd create a few months ago with most patches from Microsoft. I did get the latest patches prior to installing Vista.
After the patches were installed, it was a textbook (long) install of Vista. This is on a dual-core, 2GB machine. Good grief it takes *forever* to install. I'd say it took about an hour from start to end. I'm not complaining really, just making an observation here.