Thanks BlueEagle, we await your return.
You say "Office came installed with it's own CD".
If the PC came from a major supplier, it is likely that the software was loaded from an "OEM" source and has a product ID that is different from the CD you have.
I mention this because sometimes these OEM licences are not granted update rights by the Update Site. I read a Microsoft workaround solution to this issue just a day or two ago and, for the lfe of me, I can't rmemeber where I saw it. When I remember, or when I find it again, I'll come back with a Reference for you to read.
Meanwhile.....
Later...
Right, found it.
Office XP SP3 Full Version
and here's the text of the paragraph that described its use.
To install SP3 without the original Office XP CD
When installing SP3, you may be prompted to insert one or more of your original Office XP CD-ROMs. If you do not have access to your original Office XP CD-ROM you can install Office XP SP3 Full Version (58925 KB). Follow the instructions on the screen to complete installation. Note: Some users will still be prompted for the original CD when using the Office XP SP3 Full File Version, depending on your installation of Office XP. For more information, please see the Microsoft Knowledge Base article, (828451) OFFXP: Why Service Packs, Updates, and Security Patches May Require the Office XP CD-ROM .