Easy method to download Windows XP Service Pack 3

You can turn on the automatic updates so Windows XP can automatically download the latest updates for you:

Right click "My Computer" and choose "Properties", from the top tabs, click on "Automatic Updates", then click on the radio button "Turn on Automatic Updates".

Check for updates on Windows Updates, visit this site http://windowsupdate.microsoft.com (http://windowsupdate.microsoft.com)

Using Internet Explorer version 5 or later, click Express (Recommended). Windows then scan your system and list some updates for you to download.

You can download the whole service pack 2 or 3 from Microsoft.com, they are pretty big file. Just double click to install.

source: ehow.com