Hi Sean
Assuming the newsletter data is within joomla - if you access the database directly - the program that you use to view / access the database will usually offer an export option with a choice of format.
Also there is a component that I have not personally used, but may do what you want called Jix - view info at
www.jix.com.au
Either way, your export will be limited by how the data is currently set up in the tables - e.g. if there is now one column for name - i.e. first and last name together in one column - when you export it to excel you get the same column - name (not 2 columns 1st and last name etc)
[Don't forget to always back up your site / database - before playing with it.]
And let us know how you go,
