I'm looking for the new Sente version 5.
I add some more info below.

Sente 5 is the next-generation academic reference manager. Sente helps you find, organize, review and cite the academic literature in your field, and it does it in ways that you have probably not thought possible before. Sente also helps you build and maintain your library of PDF files for these references, because having ready access to the full text of important articles can be critical. Sente also excels at properly formatting bibliographies in your papers, but you probably already knew that.

http://www.thirdstreetsoftware.com/site/introduction.html

Thank you very much

So, so, so... I've found the solution!
This is not my work but it works just fine. I'll quote the code and then the instructions for the ones that may be interested.

#!/usr/bin/perl

use Digest::MD5 qw(md5_hex);

$ifconfigin = `/sbin/ifconfig en0 | grep ether`;
$macaddr = substr($ifconfigin, index($ifconfigin, ":")-2, 17);
$macaddr =~ s/\://g;

$sntype = "Sente5";
$snprefix = "TSS-AC-$sntype-";
$sntime = "perpetual";
$sn2hash = "ZTSSZACZ". $sntype . "Z". $macaddr . "Z" . "$sntime" . "Z";
$sndigest = md5_hex($sn2hash);

$sn = $snprefix . $macaddr . "-$sntime" . "_$sndigest";

print "\nSente 5.x Perpetual Authorization Code for this mac:\n$sn\n\n";

$licfile = "Sente 5 Authorization Code";

open (LIC, "> $licfile") or die "Cannot create the license file:\n$!\n";
print LIC "$sn\n";
close (LIC);

print "Copy the file \"$licfile\" from the current directory to:\n"
. $ENV{'HOME'} . "/Library/Application Support/Sente/License/Sente5/Mac."
. $macaddr . "/\n" . "(if the destination path doesn't exist, create it).\n\n";

And then, the very precise instructions:

1. Turn off wireless connection
2. create text file containing the perl script Beowulf supplied. (make sure it's a text file (.txt), so use a plain text editor like TextWranger rather than TextEdit).
3. Save and name the .txt file "sente.pl" as Beowulf specifies.
4. Open Terminal, type "cd" and then drag the folder you saved the "sente.pl" file to into the Terminal window.
5. To make sure you're in the correct folder/directory, type "ls".
6. If you're in the correct folder, you'll see a list of all the files in the folder that includes the "sente.pl" file. If you don't, you're in the wrong folder/directory - go back to step 4.
7. Type "perl sente.pl" in Terminal, and a file named "Sente 5 Authorization Code" will be generated in the same folder.
8. Instructions as to where to place the "Sente 5 Authorization Code" file will appear in the Terminal window.
9. Place the "Sente 5 Authorization Code" in the path Terminal stipulates - if the folders Terminal lists do not exist, create them EXACTLY where stipulated, and name them EXACTLY as stipulated.
10. Once the "Sente 5 Authorization Code" is in the correct place, select it and Get Info.
11. In the Get Info window, change the file's attributes to READ ONLY for EVERYONE, including YOU!
12. Close Get Info and select the "Sente 5 Authorization Code" file again, then Control-Click and choose "Open With" from the contextual menu. (Download and install Sente at this point if you haven't already, but DON'T open/run the application.)
13. Choose "Other" from the very bottom of the dialogue and navigate to the folder that contains Sente 5.7.1.
14. Choose "All Applications" from the very bottom of the dialogue box (otherwise Sente will remain greyed out), and choose to open the "Sente 5 Authorization Code" file with Sente 5.7.1.
13. Sente should open the file and authorize, and you're up-and-running.

Good luck! \/

Just a final consideration:
I'm working on a
Model Name: MacBook Pro
Model Identifier: MacBookPro3,1
Processor Name: Intel Core 2 Duo
Processor Speed: 2.4 GHz
Number Of Processors: 1
Total Number Of Cores: 2
L2 Cache: 4 MB
Memory: 4 GB
Bus Speed: 800 MHz
Boot ROM Version: MBP31.0070.B07
SMC Version (system): 1.18f5

running with OSX 10.5.7

...and BeoWolf is a wondeful user from another forum!