Office 2003 vs office 2007?

Hello,

1)can you identify why office 2007 is so different that office 2003 users cannot read office 2007 files.
2)im unable to find office 2007 documents by searching for .doc files, why?
3)what steps do i take to resolve this situation in the short-term?

if you could help me out with this that would be awesome!! thanx