Computer does not recognize Service Pack 3

[spadija]

I just installed Symantec Norton 360 3.0 and ran its diagnostic report. The results surprised me as it told me I did not have the latest service pack. I am running Windows XP Media Center Service Pack 3, or at least, I thought I was.

The key section of the report:

Operating System

Problem: Your operating system does not have the latest service pack.

Recommendation: Upgrade to the latest Windows Service Pack to make sure your computer has the latest security and performance patches.


This section provides key operating system details including version, timing of last update, and more.
Feature Details
Operating System Microsoft Windows XP Professional
Patch Level Service Pack 2
Date Installed 1/30/2009
Country Code 1
OS Language Version 1033
ANSI Code Page 1252
System Locale 0409
Internet Explorer Version 8.0.6001.18702
Windows Update Automatic
Latest Windows Hotfix Date 3/14/2009
Path C:\WINDOWS\system32;
C:\WINDOWS;
C:\WINDOWS\system32\WBEM;
C:\MCC18\mpasm;
C:\MCC18\bin;
C:\Program Files\Microsoft DirectX SDK (August 2007)\Utilities\Bin\x86;
C:\Program Files\Common Files\Roxio Shared\DLLShared\;
C:\Program Files\Common Files\Roxio Shared\DLLShared\;
C:\Program Files\Common Files\Roxio Shared\9.0\DLLShared\;
c:\Program Files\Microsoft SQL Server\90\Tools\binn\;
C:\VXIPNP\WinNT\Bin;
C:\Program Files\Common Files\iZotope\Runtimes;
c:\Program Files\Microsoft SQL Server\100\Tools\Binn\;
c:\Program Files\Microsoft SQL Server\100\DTS\Binn\;
C:\Program Files\TortoiseSVN\bin;
C:\Program Files\QuickTime\QTSystem\;
C:\Program Files\GnuWin32\bin\;
C:\Program Files\Subversion\bin
Latest Windows Hotfix Date 4/1/2009

A few months ago I performed a Windows repair installation, which likely left a number of incorrect registry values.
I have since installed Service Pack 3 and Windows Update gives me no further updates, but going into the system properties window also tells me that my system is:
Microsoft Windows XP
Media Center Edition
Version 2002
Service Pack 2

At the moment, this doesn't seem to be causing any problems, but I'd still like to fix it.
How can I make sure that my computer does indeed have Service Pack 3? If it does, how can I get my computer to recognize that it does?