Excel

 Hi,
I receive different excel files from clients.I have to work  on these files ,fill , and send back to them.So I need to import these files to sql,to work and to export.The clients only work with excel.How to import these excel 2007 files and export.And I wanted your advice - may be me to work directly with excel files from c# application.Not through sql?
C# program - excel files.

Thanks,
ilkin