Viewing from Excel 97 to Office XP

When I save a file on the shared drive in Excel '97, nobody can view it who
are working with Office XP? I am working with Windows 98 and Excel/Word 97.
They are working with Windows XP and Office XP. The only way I can get the
files to them so they can see them after I have saved them, is to email them.
Why can they not view them? I can see them clearly from my computer and can
read their XP files ok.