I have MS Office 2003 and Open Office installed on my workstation at work. I like to use Open Office more because I'm completely fed up with the BS I get from MS Office. And, I can save it as a PDF with Open Office without anything else.
I've used PDF995 in the past though, and it is very good. No complaints about it - PDF995 is very good.
Personally, I'm hoping that Open Office gains more momentum and that the MS monopoly on document formats erodes in favor of open standards.
But, on the plus side for MS (AFAIK), RTF is open to anyone who wants to implement it. I think a good way to do it would be with zlip because RTF documents are beasts when you use graphics. Great for text, but graphics really bloat them.
For IE, Office needs to be installed on the client. And, AFAIK, the doc viewer from MS has not been updated since 1997~! Does anyone know otherwise?