It is interesting what you say about the macro language. It cannot though be entirely incompatible because all the macros I had recorded, to make working quicker, in Word 97 (the version of Word that I had previously used on my old computer) and assigned to toolbar buttons (including custom drawn buttons) and which therefore modified the Normal.dot template, worked in 2003 by the simple step of copying the Normal.dot from Word 97 to the correct location for 2003 on my new computer.
Although technically, the Word/Workbench integration is based on macros, this is far more complex than self-recorded macros. I'm not fully familiar with all technical details, of course, but there were changes to the file/macro/data structure in Office 2003.
After seeing your reply I searched this forum and found that a lot of people had encountered this problem and had wanted to use Trados5.5FL with Word 2003 when this started to take over from earlier versions. I would have thought therefore that Trados or someone would have created a new TRADOS5.dot that was compatible with Word 2003. But clearly Trados decided to force people to upgrade!
When T5.5 was developed, Word 2003 had not even been communicated (let alone its data model published) - hence, the templates developed at the time could not have anticipated later versions of Office.
Going back to an earlier version of Word is not an option.
...in which case you will need to use a later Trados version.
Microsoft already regard 2003 as out-of-date and are pushing the 2007 version, despite this getting a very mixed reception.
Indeed - which is why I bought several Office 2003 licenses (plus a couple of Win XP Pro licenses) when they were still on sale...
[Edited at 2008-08-13 16:03]