When you delete it from the recycle bin, you are really only deleting the pointer to the file...the file actually remains on the drive and can sometimes be recovered.
There are various programs that can do this....plus there are various programs that can truly and deeply shred the file address (for lack of a better word) and the actual clusters the data reside in. Even these can be sometimes recovered, depending on how hard you want to work at it.
Here's one:
http://www.heidi.ie/eraser/there are many others