Resulting difference between 2 directories

[Gerard Samuel]

The scenario.
I have 2 snapshots of a CVS repository (old & new), and I would like to 
execute a script/command that goes through the directories, and produces 
another directory, that contains, the difference of the 2 directories where 
it contains all the newer files/directories.
So basically, Im looking for a way to just get whats changed between the 
snapshots, so that it can be distributed.
Now this scenario does not have to be restricted to just CVS snapshots, it can 
be any 2 directories.

I can probably come up with a php script that would do as described above, but 
Im checking with the list to see if there are any already available 
tools/ports, that I can use to accomplish this task.

Thanks