Generally, when data is deleted the space is considered "free" by the system. The actual data is still there but the markers for the data have been removed. This then allows the drive to overwrite it, basically.
In addition to the above posters software suggestion, you can also try the following:
System Restore (which might or might not work. Usually doesn't but it's an option)
Check the recycle bin (although files of that size are generally deleted and not stuck there)
R-Undelete - pretty good software for recovering data. Had a client lost a big chunk of her stuff and this helped me restore about 60% of it.
As a rule however, unless you have a backup someplace, the odds of being able to recover deleted directories, especially when you have used the PC after the fact, are slim to none I am afraid without costly software to do so.