I was looking for a lightweight, easy to use systems performance log for a Debian 5.5 server and came across Webminstats
Systats is a Webmin module that tracks cpu, memory, disk and io statistics over time.
It doesn't install without a few additions to the standard Debian install.
Of course you need Webmin installed, and then perl. Once you've installed Webmin and perl on your systems, run the following command lines (as root or sudo) in your shell BEFORE you attempt to install systat: