The best program out there is GetDataBack NTFS and FAT32 editions, if you are running windows.
Steps:
First, stop using your computer immediately and shut it down.
Take out the hard drive and install it as a slave on another computer with GetDataBack installed.
Run the Program and if the data wasn't directly overwritten when the OS was reinstalled (which is actually fairly likely, because if you reinstalled the same OS it likes to install on the same parts of the HD as your old one, and thus, not where your documents are.
The data can then be recovered onto the computer you are using to get data off of the HD.
The problem with this approach is that GetDataBack runs about $80. But it's well worth it if you really need some of the data on there. Or of course, cough cough, cough.. uh hem. Anyway, I've used the program sucessfully in a situation very similar to yours (parent's forgot about some of the necessary data until after the reformat :) and it worked perfectly)
~Lyuokdea