About Windows Installer, the .NET Framework, and Visual Studio.
The .NET Framework 2.0 and Visual Studio 2005, along with SQL Server 2005 and BizTalk Server 2006, will be officially launched November 7th. .NET and Visual Studio, at least, will require that you have Windows Installer 3.0 installed on Windows NT-based platforms, including Windows 2000, Windows XP, Windows 2003, and newer. If you have Windows XP SP2 installed you have at least Windows Installer 3.0. If you have Windows 2003 SP1 installed, or you have Windows XP or Windows 2003 for x64 then you already have at least Windows Installer 3.1.
For reasons that affect servicing, patches for .NET and the Visual Studio line of products including the future release of Team System will require Windows Installer 3.1. Downloading Windows Installer 3.1 and installing it now may save you trouble later and .NET and Visual Studio will still install correctly since Windows Installer does a good job of being backward compatible, at least as far as Windows Installer 2.0 in terms of some behavior.
And speaking of Windows Installer 2.0, Windows 98 and Me users are required to have Windows Installer 2.0 installed. Both shipped with Windows Installer 1.2 so you'll need to download Windows Installer 2.0.
In both cases the setup bootstrap will provide a link to download the appropriate version of Windows Installer - either 2.0 on 9x or 3.0 on NT - if you don't already have it installed.
How to install multiple patches at once to save time.