Just open excel (or any other option like LibreOffice Calc) and go to File/Open and select your .csv file
A wizard will be launched where you will be able to select the desired separators for rows/columns and that is it, the program will do all the work.
I use "
as text delimiter, ;
as separator and 'UTF-8' as encoding.
You can also select in a previous that will see every column and select the type of it (e.g. date, text).
This works for me using LibreOffice Calc, it might be suitable for you to, but maybe you have to change a few details, but the overall picture looks the same.
After that, to save the file again as a .csv to import into OpernERP, just go to 'File/Save as...' and select .csv where it says file format (or something like that, the place where you can choose the extension of the file).
Hope it is the same with Excel (or at least that you can figure it out from this tips)!