CentOS

Unlike Top, its newer sibling - Htop is better in every way. It provides more detailed information, supports colours and is more configurable. Htop is available in the repositories of most distros. However, CentOS (and therefore, RHEL) is not one of them. While it it apparently available in the EPEL repositories, I could not find it for CentOS 4.9. In any event, what we have below are the (simple) steps to install it from the source packages:

I ran into the following warning while trying to install a package from the IUS third-party repository for CentOS:
warning: ius-release-1.0-6.ius.el5.noarch.rpm: Header V3 DSA signature: NOKEY, key ID 9cd4953f.

This was caused because the IUS GPG key was not (correctly) installed. To fix, type:
sudo yum install yum-plugin-replace

This should prompt you to download and install the correct key. Once this is done, the installation of other packages should proceed smoothly.

CentOS 4.5 (final)
Plesk 8.2

When I ran YUM to update my server, I ran into a dependency error:
Error: Missing Dependency: glibc-common = 2.3.4-2.25 is needed by package glibc-dummy-centos-4

CentOS / RHEL 4 ship with a rather dated version of Subversion - 1.1.4, and according to a result from google, upgrading it to the latest stable was not possible due to incompatibility with the shipped version of APR [0.9.4]. However, this might not be the case.