with mouse on file right click, select "Open With>Chose program" there you select the software you want to open .csv files, if you want to make default everytime you open file, check option "Allways use the selected program to open this kind of file"
Hope this help.
André Lage Microsoft SharePoint and CRM Consultant
Blog:
http://aaclage.blogspot.com
Codeplex:
http://spupload.codeplex.com/