I will have a very large document with plenty of highlighted text. Is there a macro/plugin/add-on/etc. for Microsoft Office 2003 that can prepare a report or even a list of all the highlighted items?

Depending on what you've got, you might be able to use Find/Replace to delete everything that isn't 'highlighted'. Note that there's a significant difference between what Word regards as highlighting on the one hand, and colouring/bolding/selecting text on the other. Many many users seem to think the latter is the same thing; it isn't.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]