You have an XPS 400.

The error code -29 indicates that the platform is not supported. 

DSC is for Specific Models of Vostro and Consumer Dell's

If your model had Dell support center before it must be upgraded to version 3.0

This is not a fix however for an unsupported model.

Identifying Dell Computer Models Using the Model Code - KB Article - 296718

On Sept 26, 2005 the System Setup program on certain Dell Dimension™, Inspiron™, and XPS™ computers was changed to display a model code instead of the computer model name. The Resource and Driver CD also lists the computer by this code. This may cause confusion when identifying which device drivers to install. If you are unable to identify your computer using the model code, refer to Table 1 below to determine the model name of your computer.

Table 1: Model Names and Codes

WindowsUpdate.log shows:

dfc      Agent        * WARNING: Online service registration/service ID resolution failed, hr=0xC80003F3

dfc      DtaStor      FATAL: Failed to initialize datastore, error = 0xC80003F3

dfc      Agent        * WARNING: Exit code = 0xC80003F3

That means you may need the latest FULL DOWNLOAD service pack.  If you have XP that would be SP3.

Download: Windows XP Service Pack 3 Network Installation ...

My Model Code is DXP051, what  am I to do to fix my stated problem, I am not understanding what you are saying.  Sorry but I am lost.  What am I to do with this Model Code to fix my computer to work with Windows Update and Dell Support center?

Also my computer say that it is running Microsoft Window XP, Media Center Edition, Version 2002, Service Pack 3

Also a message the say

rundll32.exe - Application Error

The application failed to initialize properly (0xc0000142).

Click ok to terminate the application

This keeps appearing when I open different things.

The error code -29 indicates that the platform is not supported.

XPS 400 is code DXP051