What problems are you having ?
Without knowing that, I think it will be really hard to figure out what is happening.
My dear when ever ur saving a file in office 2007, then the file extension the file gets is filename.xlsx
now when u open this file with lower version of office this file is not accessible. so what u have to do is save the file with save as option and use office 97 to 2003 compatible. Hope this will solve ur problem. Ahmed