Why? Well, it took some digging to find out, but apparently MS, in its infinite wisdom, decided to stop using the IE HTML engine to render Outlook emails. Now Outlook 2007 uses....MS Word's HTML engine. Really.
-johnk
The infinite wisdom presumably came from the constant criticism in the past of ActiveX/Java based viruses arriving in emails because of the holes in IE's rendering engine.
Trouble is using Word is just shooting themselves in the foot big time. Maybe someone should suggest Firefox - or allow users to choose the rendering engine. It is, after all, rather reinventing the wheel when most people will have multiple engines installed already!!
Anyway, thanks for the heads up - I wasn't totally convinced about the upgrade to the ribbon interface but this has finally convinced me to leave it at Office 2003 which works fine.
Not sure about PST backward compatibility but Office 2007 comes in various flavours - some of which don't include Outlook 2007. Why not uninstall Outlook 2007 and go back to Outlook 2003 which should coexist quite happily with the other Office 2007 apps.
Before you do it however I would strongly suggest that you export all mail to Outlook Express from every PST file you have opened in Outlook 2007 because I think they changed the PST format between versions and also your contacts (you can import it back in to Outlook 2003 if you need to).
I'm not sure how you could salvage other data types such as tasks, calendar etc. but you may be able to export them in a CSV file or Excel file.
Whatever you do backup your PST files before messing then at least you can return to Outlook 2007 if you feel it is causing problems.
IIRC when they gave out the public beta and RC1 and 2 of Office 2007 it didn't install Outlook 2007 because of backward compatibility issues.