Without a backup, your options are not very promising.
You can try using a data recovery application such as Data Rescue. ProSoft Engineering provides a free trial version.
http://www.prosoftengineering.com/pr...ata_rescue.php
Note that the more you use your system and hard drive, the more likely the area on the hard drive where this data was stored will be over-written by other data making recovery by any means impossible.