http://support.microsoft.com/kb/322389/

I don't see a link for getting service pack 2 on a CD.

Can't get an SP2 CD from MS anymore.

But you could download the SP2 package and just burn it to CD yourself - then copy it back to the hard drive when you're ready to install it:

http://www.microsoft.com/downloads/details.aspx?familyid=049c9dbe-3b8e-4f30-8245-9e368d3cdb5a&displaylang=en

Use nlite. Insert your XP CD into the computer, go to my computer, right click the CD and click explore select all the files (control and a) and then copy (control and c) and paste (control and v) to a folder on your desktop and call it XP.

Download the standalone XP Service Pack 2 and save it to your desktop.

Download the standalone XP Service Pack 3 and save it to your desktop.

Open nlite, select the XP folder under your desktop. Select Service Pack under integrate:

Select the service pack 2 on your desktop and then close nlite.

Repeat with the service pack 3.

Then select create bootable iso.

Once thats made, use a program such as Roxio to burn the image to a blank CD which will give you an xp service pack 3 bootable CD and you use that CD as if it was the original. Except will be updated with Service Pack 3.

You may also want to experiment with the tweaks and autoattended but create an uneditted one with just the service packs slipstreamed incase you run into problems.

Can you just install sp3, since it is the latest update? 

http://support.microsoft.com/kb/322389/  says  in More Information:

To install Windows XP Service Pack 3 (SP3), either Windows XP Service Pack 1a (SP1a) or Windows XP Service Pack 2 (SP2) must already be installed.

But http://www.microsoft.com/downloads/details.aspx?FamilyId=68C48DAD-BC34-40BE-8D85-6BB4F56F5110&displaylang=en  (sorry, it doesn't appear as a link.  Don't know why, but copy to a browser) says::

Windows XP Service Pack 3 Overview

Brief Description

Windows® XP Service Pack 3 (SP3) includes all previously released updates for the operating system. This update also includes a small number of new functionalities, which do not significantly change customers’ experience with the operating system. This white paper summarizes what is new in Windows XP SP3. You can obtain Windows XP SP3 from Windows Update, at http://update.microsoft.com.

I just used sp3, which I purchased from Microsoft, and it seemed to install ok.

Jim