I have come across yet another Vista bug - quite fundamental and one which MS are aware of as they even offer a fix - (which hasn't worked for me or many others). Office 2003 cannot install any updates. On day one of Vista Install 2 Office updates have been installed. However, since then there are no less than 13 security updates which cannot be installed due to problems with "Office Source Engine". You name it and I have tried it - short of performing a complete uninstall which I daren't do just in case I cannot reinstall again and don't fancy paying nearly £400 for Office 2007. Office is a Microsoft core product and one would have thought they could sort out their own software to run with Vista 
