Current versions of vzdump has dependency for cstream and perl-LockFile-Simple, both available via rpmforge. Below is how I got it to install and run on CentOS-5.5 x86_64 architecture.
rpm -ivh rpmforge-release-0.5.1-1.el5.rf.x86_64.rpm
yum --enablerepo=rpmforge install cstream perl-LockFile-Simple
rpm -ivh http://download.openvz.org/contrib/utils/vzdump/vzdump-1.2-4.noarch.rpm
It's necessary to export the location of the PVE libraries that vzdump requires. This can be added to ".bash_profile":