UN*X (or Mac OS X) utility to retrieve deleted data

[José Pedro Sousa do Amaral]

Hi,
Could someone be kind enough to point me toward a program, method, or  
more appropriate forum that can help me retrieve data from an erased  
4 GB Compact Flash card? I use a USB 2.0 multicard reader under Mac  
OS X (10.4.9 on Intel) to read and process FAT32-formatted Compact  
Flash cards with sound files recorded by a Marantz digital sound  
recorder. That setup records three minutes on the hour sound episodes  
from a pond; we are conducting a behavioural study on anurans in said  
pond.

Last week, someone stole our field laptop that contains last week's  
data and now we are trying to retrieve those data from the Flash  
Card, which has since recorded over with this week's data. My  
colleagues and I have a mix of Intel- and PowerPC-based Macs running  
Mac OS X; we have limited access to machines running Windows and Linux.

Therefore, I am looking for UN*X programs (or Mac OS X) or methods  
using an already present tool that can retrieve erased data.

Thank you. Cordially,
ZP
--
José Pedro Sousa do Amaral

Cynic, n.:
         A blackguard whose faulty vision sees things as they are,  
not as they ought to be.  Hence the custom among the Scythians of  
plucking out a cynic's eyes to improve his vision.
                 -- Ambrose Bierce, "The Devil's Dictionary"