Office 2007 uses a different file format than Office 2003 to store documents. As a user of Office 2007 you need to be aware of this. For example, if you create a new Word document and then save it, by default Word will save it as a '.docx' file. Many users of older versions of Word won't be able to open that file. An alternative would be to use 'Save As' to save the document as a Word 97-2003 Document, which would be a good, old '.doc' file.
Where's my menu gone?Another change with Office 2007 is that the menu has been replaced with a 'ribbon toolbar'. This is pretty self-explanatory except perhaps for one point. What was on the 'File' menu is now accessed by clicking the round button that sports the Office logo. (The shortcut key Alt-F will still work for accessing these options).
The online documentation for Office 2007 is really comprehensive. That should be your first port of call. If you are still stumped then come and ask me. I am just starting off with Office 2007 myself so we can learn it together.
Alan