Linux, Yum update issue

I perform a yum update and get the following at the  end

Transaction Summary
================================================================================
Install       4 Package(s)
Upgrade     369 Package(s)

Total size: 471 M
Is this ok [y/N]: y
Downloading Packages:
warning: rpmts_HdrFromFdno: Header V3 DSA signature: NOKEY, key ID 897da07a
rhel-x86_64-server-5/gpgkey                              | 1.1 kB     00:00


Public key for NetworkManager-0.7.0-13.el5.i386.rpm is not installed
[root@rhel yum.repos.d]#

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I assume this means the update did not work

What does it want me to do, and how do I do it ?

Thanks