No right to open file once copied on the desktop

It sounds like you are using a non-server Mac to act as a server. Is this correct? If so I highly advise you to upgrade to some version of OS X Server.

If I am correct, your issue is caused by using standard Mac (or POSIX) permissions to handle your file share. This is the only option you have for a standard Mac when sharing files. This causes permissions issues, whether you are using AFP or SMB protocols (though SMB is worse in this respect).

If you can upgrade to OS X Server, you will want to first clean up permissions on the folder you wish to share (thus fixing any existing issues). Then create users & groups to model your organization structure. From there you will create a new file share using the Server app. Don't change any of the default permissions it gives. Instead click the "+" button to add a new Access Control Entry. This is a special type of permission that OS X Server can grant, and it resolves all of the permissions issues a standard Mac will give you in such a setup.

Peachpit Press offers a great write-up of all of this in their OS X Server manuals as well, though I couldn't find anything to link to directly. I hope this helps.

There are known issues (Apple-created bugs) with several revisions of OS X 10.5 Leopard Client and AFP file access, including permission problems and in certain cases even the potential to lose or overwrite files completely.

There is no work-around for these bugs, they are in the operating system itself and can be reproduced on 2 freshly-formatted & installed Macs running Leopard 10.5, and most or all of the later revisions, i.e. 10.5.1, 10.5.2, etc.

Your best solution is to be sure to update all 10.5 Macs to 10.6.8 Snow Leopard. Failing that, updating everything to 10.5.8 (the last release of Leopard) may solve your problems.

Here's a list of references that go into more detail:

http://support.grouplogic.com/?p=1508

https://discussions.apple.com/thread/1423847

http://www.insanelymac.com/forum/topic/67625-preping-for-105-permissions-issues-with-afp-shares/

http://lists.apple.com/archives/macos-x-server/2010/Dec/msg00267.html

http://www.mailinglistarchive.com/html/[email protected]/2008-07/msg00409.html