Later versions of WinXP were distributed without Microsoft Java, something to do with legal issues with Sun. Sounds like your version of WinXP is one of these.
The legal issue, so I am aware, has now been resolved and SP1 (service pack 1) contains the required Java files. Your problem sounds like your version of XP was activated with an invalid key. Windows Update tries to read this as part of the SP1 installation/upgrade and stops the process as a result of this.
This leaves you with 2 options:
1. Purchase a full license for WinXP and re-activate
, or
2. Forget about SP1, download the Java files from the Sun site that work with your pre-SP1 version of XP (I can't remember the URL off the top of my head - I will post it later tonight).
Hope that this makes sense
