POI can be handy for writing Excel documents. It has some functionality with Word .doc files as well if you're interested, but that part of the api is not quite up-to-snuff yet. Their priority seems to reside with Excel which is where most of the interest probably is anyways.
Dad always thought laughter was the best medicine, which I guess is why several of us died of tuberculosis. -Jack Handy
If you need to do formating within excel I would recommend the POI API that is provided by Jakarta. I used it on my last assignment, but be careful. There are still a couple bugs in it. One of the problems that I noticed is if I user were to scroll thru blank cells in the excel spreadsheet with the cursor, the API would bomb out because of null reasons. You would of thought they would of checked for null values. I would always have to highlight blank cells and delete them in order for my processing to work. The CSV appoach works great too if you do not intend to do any formatting with the excel spreadsheet.
Good luck, Ryan
SCJP 1.4, SCWCD
Java: The power, elegance, and simplicity of a hand grenade