Updating Windows machines which are not connected to the Internet has always been an issue, especially when it is a new install and there are dozens of security updates to find, download and install.
Torsten Wittrock (formerly Heise Security) has published a very handy open-source tool to make all the process (almost) easy, called "WSUS Offline Update".
Detailed presentation: http://www.heise-online.co.uk/security/Do-it-yourself-Service-Pack--/features/80682
Use it first on a Windows XP machine which is connected to the Internet to download all updates for every needed version of Windows and Office. Then burn the CD or DVD ISO image, or copy the "client" folder to a removable disk.
On the target machine, launch the updater. The option "automatic reboot and recall" is very useful to save time, but it may not always work. You may also encounter some issues if the machine is hardened, for example you might need to enable the "Automatic updates" service if it was disabled. If for any reason one patch fails to install, it is usually a good idea to launch it directly to get all the error messages.