I\'m a bit confused here.
When I use Excel 2003 to export a sheet to CSV, it actually uses semicolons ...
Col1;Col2;Col3
shfdh;dfhdsfhd;fdhsdfh
dgsgs
As mentioned by dendarii, the CSV separator that Excel uses is determined by your regional settings, specifically the 'list separator' character. (And Excel does this erroneously in my opinion, as it is called a comma seperated file)
HOWEVER, if that still does not solve your issue, there is another possible complication:
Check your 'digit grouping' character and ensure that is NOT a comma.
Excel appears to revert back to semicolon when exporting decimal numbers and has digit grouping also set to a comma. Setting the digit grouping to a full stop / period (.) solved this for me.