Hi,
I'm not sure about the import into Excel with commas in the text, fixing that sounds like it would be the best solution. But to stop someone from entering a comma character add the following JavaScript into the change event of the text field;
xfa.event.change = xfa.event.change.replace(/,/g,"");
This uses a RegEx (the bit between the "/" characters) to replace all occurances (because of the "g") with an empty string (the second parameter to the replace method).
Regards
Bruce