In the last couple of days I tried to install Visual Studio 2005 on my freshly installed Windows XP (service pack 2). Nevertheless I could get the job done, since the installation failed with the message “Could not install MS XML 6.0 parser”. When I ran the seperate MS XML setup (located on cd in \vs\wcu\MSXML\msxml6.exe), the setup told me that it was already installed. HUH? The some sort of deadlock situation kept me puzzled.
Finally I managed to install VS2005 with a work-around (bypassing the MS XML 6.0 setup). First I installed the .NET framework 2.0 and MS XML 6 (I already had this one). After that I installed VS2005 without the pre-requisites packages. This can be done by launching the setup via the command-line:

\vs\Setup\setup.exe /NO_BSLN_CHECK.