The release of Windows XP SP3 was shelved to the first half of 2008 which is quite a long way to go. It could be a tedious task to install all the updates released after SP2, especially when you do not have an Internet connection or you're building 10 computers. Slip-streaming security updates into XP SP2 on the second Tuesday of every month is also quite discouraging.

However, you can download ready-made installer package from autopatcher.com which has all the security updates from Microsoft since Windows XP SP2 and is updated every month embedding new fixes that Microsoft released in the previous month.