You should be concerned only if your company has not already upgraded your workstation PC from Windows XP SP1 to Windows XP SP2. Because of all the new features in Windows XP SP2, Microsoft created a special SP2-blocking tool to allow corporate IT departments to test the service patch before automatically downloading it to corporate computers. On April 12, that blocking tool expires. So, if you are on a desktop or laptop within a corporate network, and if your company uses a Windows automatic update service that connects directly to Microsoft servers, beginning at midnight on April 12, 2005, your desktop or laptop will become eligible to download and install the security update--whether or not your company is ready. The risk here is that some network connections and/or custom software might not be compatible with Windows XP SP2.

Also, once you begin the update, be sure to allow enough time for it to complete before disconnecting from the Internet. Not every enterprise uses Windows' automatic update, however. Companies that use third-party services or have their own update services to roll out security patches will not be affected by the April 12 deadline.

Source: http://reviews.cnet.com