Here's a post that should help you if you need to implement older Office file types after installing Office 2003 Sp3 :
In the post you'll find some handy .reg files that will re-enable the older file formats without having to go in and hack the registry (always a good move).
Here are the closing comments from the post (from Microsoft of course):
In closing, I want to emphasize that we're not removing support – we're making the default safer. If you're among the users who do need to be opening these formats, we will continue to support you. We also recognize that we have not made any of this as usable as we'd like, and we apologize that this hasn't been as well documented or as easy as you need it to be. We're also going to take a hard look at how we can do better in the future.
Now I know that Microsoft is screwed no matter what it does but don't you think Microsoft, that a warning dialog box during the install of the Service Pack might have been a good idea? Hmmm? If there was one then I could understand your 'making it more secure' claim BUT keeping this thing hidden or as you euphemistically put it "hasn't been as well documented or as easy as you need to be", then I gotta say that my BS detector is flashing big time, since it appears more likely you are trying to force people into the new versions of Office. Now while that in itself is not a bad thing and necessary to ensure we are all safer, one would again tend to think that the way this has been conducted is more along the lines of benefiting stockholders rather than users. Maybe?