Yes I did read that, and it meant not a lot at the time, although I did re-install and ensured everything was as it should be under my current user name etc.
BUT having just skimmed it again, I think I may know what the problem is... not sure, but perhaps it's because I installed office 2003 via my home CD (home edition) But Infopath was installed on my PC by my works IT Dept (I work half from work and half from home) so maybe they installed the Professional Edition?
Bugger me, I wonder if that's it? Off to investigate.