How can I view delete files? If that space has not been overwritten yet.

As far as I am aware, no Unix filesystem provides "undelete" capability. Sorry.

How does the FBI do it then?

Surely the data is still on the drive immediately after the file was deleted.

Is there an open source software package that lets me view files (data on the drive) not listed with the ls command?

Checkout the forensics section in security references thread. There are a number of links on "undeletion" including a number of tools used in forensic file recovery. Ease of recovery depends alot on your type of filesystem and some of the tools are less than user-friendly, so your mileage may vary.

Google is your friend

http://www.google.co.uk/search?hl=en...e+Search&meta=

Howzit

The easiest way to explain this is in the following manner. Imagine a filing cabinet and in each draw u have a indexer so that you are able to find the location of the file. When u delet a file it removes the indexer therefore the file still remains on disk. When you copy a new file onto the system because that area is no longer marked by the indexer the file may be copied to the same area and if that happens then the file is lost for good. If the file gets copied to another area then the original data still remains in that area which then with special tools you are able to recover that data from the disk.

Hope this helps

Cheers
Tony

Which one has the best interface to view a windows harddrive?

Has anyone used:
http://www.sleuthkit.org/autopsy/download.php

Depends on what you prefer, but Autopsy has a GUI interface and has support for NFTS and FAT partitions. TCT would go under "not particularly user-friendly". Here's also a brief review of it (Autopsy):

http://www.informit.com/guides/conte...eqNum=107&rl=1