Francesco,
To help me define my issue further, please run this command on your CentOS5.9 box & post your result.
#strings /usr/lib/libstdc++.so.6 | grep GLIBC
I'm running newer versions of all the c-libraries you are, but I'm still missing the GLIBC libraries requested by Landesk agent ... So I'm wondering if your Landesk agent needs GLIBCXX_3.4.11.
I have
glibc-devel-2.5-118.el5_10.2
glibc-headers-2.5-118.el5_10.2
glibc-common-2.5-118.el5_10.2
glibc-2.5-118.el5_10.2
openssl-0.9.8e-26.el5_9.1
openssl-devel-0.9.8e-26.el5_9.1
libstdc++-4.1.2-54.el5
libstdc++-devel-4.1.2-54.el5
If it helps, my installation process was to create the Linux_x32 installer on the Landesk Server, scp the files to the client, login as root, chmod the executable, and run the installation. (Paul's process was to smbmount the Landesk folder on the same client & run the same files as the same user.)