If you formatted the drive and did a 'clean installation' of Windows, it's unlikely that you'll be able to recover any data. (Some data can survive a disk format but you'd probably need the services of MI5 to retrieve it. It's beyond the scope of most file recovery software).
If you did an 'on top' installation of Windows, you shouldn't have lost any data. However, if you want to see if your old files are there, try searching for *.pst (That assumes that you're using Outlook and not Outlook Express. For the latter, search for *.dbx).
Such a search should bring up all your current Outlook files, such as Inbox.pst. However, you might find that the old files are there as well. They might have the same names (but be in different folders) or they might have been renamed to something like Inbox(1).pst.
If the old files are there, you need to replace the new files with the old ones (i.e. you'll be replacing an empty Inbox with the old one with your e-mail in it).
If you can't find any old pst files, it's almost certain that all traces of your old data have been deleted. Sorry!
Chris