You need Microsoft Windows XP Service Pack 2 for the following reason:
When accessing the Internet, your computer is vulnerable to viruses. A failure to patch just one known security vulnerability can leave your computer wide open to Trojans. These nasty little programs seek out unpatched computers and allow attackers to use your computer without your knowledge. Trojans may use your computer to start denial of service attacks in which they try to disable Web sites by overloading them with traffic from thousands of Internet users. You may never know that your computer is being used by a Trojan.
Microsoft Windows XP Service Pack 2 provides an enhanced security infrastructure that defends your computer against viruses, worms, and hackers, along with increased manageability and control and an improved experience.
Installing a Microsoft Windows XP Service Pack 2 provides a wider coverage on the fixes and enhancements for your operating system instead of the small quick fixes that patches are designed to address.
More information can be found in this link. http://support.dell.com/support/topics/glo...9836&l=en&s=dhs
Hope this helps....