How to Import Data from a .CSV or .XLSX file to an AS400 file?

I want to import the data of a .CSV or .XLSX file to a AS400 file. How can I accomplish this? Also, the .CSV/.XLSX file has two columns that I would like to keep in the AS400 File. Any inputs would be really appreciated.

file format or extension invalid

after using Excel 2007 for several months with no problem, I had to reformat and reload windows xp professional. then I installed Excel 2007 and now I can't open the xlsx files created by Excel 2007. I get the error in the above title box. Any help will be welcomed. Gervis.