yum clean all; yum update;

this is the final output when it finished to download package:
Total 2.0 MB/s | 176 MB 01:29
Running rpm_check_debug
Running Transaction Test
Finished Transaction Test


Transaction Check Error:
package gnutls-1.4.1-3.el5_3.5.x86_64 (which is newer than gnutls-1.4.1-3.el5_2.1.i386) is already installed

Error Summary
-------------


Please help.

Hi !

Try this:

rpm -e gnutls --justdb

this will remove the rpm in the db only and allow you to upgrade it ...

do you think that this is a safe way to solve this problem?

seeing as cent 5.4 IS NOT OFFICIALLY OUT and the servers ARE NOT SYNCED YET
that is your problem

wait a few weeks AN REINSTALL . As far as i know that early release iso is incomplete.

Well, that depends on your comfort level, personally yes I would.
Working out these kinds of problems would generally involve uninstalling packages at some point, I have used this method often with good results.

You could always consider a backup of the files you might lose (I do !)

Here is an example way to backup the files that got it installed from a particular rpm, and results in the file /tmp/backup.gnutls.tar.gz :

root@f11 tmp]# rpm -ql gnutls > backup.list && tar -T backup.list -czf /tmp/backup.gnutls && ls -l /tmp/backup.gnutls.tar.gz
tar: Removing leading `/' from member names
-rw-r--r-- 1 root root 419936 2009-10-22 20:46 /tmp/backup.gnutls.tar.gz

rpm -ql package - shows the files installed by a package