There are three paths that can be followed
with the Windows Vista Business upgrade DVD:
1) Upgrade from Windows XP SP2
2) Upgrade from Windows 2000 SP4
3) Clean install
The upgrades will preserve programs & settings; at least to the extent that they are compatible with Vista. The clean install will move the prior OS files to windows.old and then proceed with the install, which will discard any installed programs or settings.
In my case, I had already installed Vista Ultimate RC1, but since Ultimate to Business is actually a downgrade, I could not use the "upgrade" path -- so I did a clean install of Windows 2000 with SP4 and then proceeded with the Vista installation.
The install went quite well, it seemed more organized than the RC1. The entire process took less than two hours, start to finish, including the requisite trip to Windows Update for several critical updates.
Next task -- installing Office 2007 Professional.