Files not open

Hello,
i have installed microsoft office 2007 on my laptop. it is working properly on my pc.
when i copy a 2007 file in my pc, i can't read my file.in my pc i have installed 2003
on my pc.how can i open my file in 2003 without installing compatibility package
please reply me on my id (karan.luthra5004@gmail.com)
thanks