"Deleting" a file doesn't actually delete it; it just marks the space as available to be used. There are third-party programs that can sometimes recover deleted files. The problem is that the space used by the file is likely to become overwritten very quickly, and this makes the file unrecoverable.
So your chances of successfully recovering this file is decent if you try recovering it immediately after deleting it, and rapidly go downhill from there. If you've been using the computer since then (for example to write this question and read this answer), your chances are probably very poor by now.
But if the file is important enough, it's worth a try anyway. Stop using the computer in question immediately, if you haven't done so already. Download an undelete program on a friend's computer and bring it yours on a floppy to try.
If this fails, your only other recourse is to take the drive to a professional file recovery company. This kind of service is *very* expensive and may or may not work in your case.
