There's quite a few bits of software that will recover deleted files. I use a program called Tuneup Utilities which has that function as one of the many things it does. Never had the occasion to use the undelete yet but from what i understand, the chances of recovery are pretty slim unless you do it straight away.
When you delete something it doesn't actually get deleted until the space it occupied on the drive is used by something else. So if it's been a while then you're likely to have used a few programs, downloaded data etc. The longer you wait then the less chance you have of getting it back complete or even at all.