I’ve managed to get the export to produce a tab-separated txt file that Excel can read by making a few changes in the Freeform code.
I’ve attached a modified version of the mcp.freeform.php file (for version 2.7.1) if it’s any use. (zipped because php attachments are not allowed)
The changes are in the function ‘export_entries’.
Each change is surrounded by comments ‘START EXPORT FIXES’ and ‘END EXPORT FIXES’.
The changes are:
(1) Comment out all the MSIE-specific stuff regarding headers, as this seems to make things worse rather than better.
(2) Remove carriage-return and line-feed characters from the field data to prevent premature line ends.
Maybe Solspace can comment on the validity of these changes, but they seem to do the trick for me, using IE7.