HELP!!! Can I get back files from a folder that has been copied over?

Question

I had a file in the trash with the same name as a file on my desktop. I accidentally started copying it from the trash to my desktop. It erased some of the files I had on my desktop in that folder that were very important, before I could stop it from copying. Is there any way to get the files back? They had been on my desktop for a few months. I'm thinking that maybe they are stored somewhere on the computer. I tried a search but came up with nothing. I usually back up to a external hard drive but I didn't this time and I'm paying for it now!

Answer 1

When a file is erased, the space on the drive that the data occupies is not necessarily erased. It is just unallocated, so that other new data can use it. However, until that new data overwrites that same physical space on the drive, your old data may still be recoverable.
To do this, you need to use a data recovery tool. There are tools that specialize in data recovery, such as
http://www.prosofteng.com/products/data_rescue.php
and other tools have a have multiple functions, including data recovery
http://www.micromat.com/index.php?option=com_content&task=view&id=202&Itemid=107
If you want to try recovering the data using such a tool, you should stop using the Mac (or use it as little as possible). Any use of the Mac will make it more likely that the space occupied by the old data will be overwritten. If that happens, the portion that is overwritten will not be recoverable.
This is a good example of when Time Machine (part of Leopard and Snow Leopard) would be extremely helpful. It does backups to an external drive automatically, in the background, once per hour that the Mac is active. You just set it up and then forget about it. You can get any file back that you accidentally erase, even an older version of it.