Office2003 SP2 and SP3 issued long ago might be on your machine if you saved them
Security updates - most unlikely, though you can see in Control Panel - Add/Remove programs - with the Show updates button checked - if they're listed under MS Office. But I think that's really useless information since the updates change the Office applications, and if the applications aren't there and you revert to the original, there is no way on earth the applications can be updated.
If you run Windows update manually it examines your computer for what's needed.
About 2 years ago I had to reinstall Office and that's the route I took.
They will not push the old, old updates which they bundled into SP2 and SP3, so while all this takes eternity, you will end up with all the updates you need.