Many, many people have been plagued by the co-existence bug that occurred when you have Office 2003 on your PC and you install an Office 2007 component such as SharePoint Designer 2007.
Suddenly, your browser would crash when you tried to open a document located on a SharePoint site.
I had a Premier Case open with Microsoft to resolve this as we were able to reproduce the error at will.
I published a workaround for the problem some time ago.
It tested fine and it is now available with an accompanying KB article.
So come and get it kids!