Saving information to an Excel file

I have an application where I need to update an excel file with the value of a text field.

Several users are using this application so when "Update" is clicked a new excel file has to be opened. The second time "Update" is clicked the value of the text field needs to be added to the already opened excel file.

Is this possible at all or would you recommend me to use XML?

The requirement from my customer is, that the data has to be transferred to a file (he prefers Excel) so it's possible afterwards to manipulate the data.