You can collect and report a lot of system activity with the command "sar".
This tool is commonly used on all kinds of Unix systems.
For example, if you want some I/O reporting you can use the command "sar -b 1 10", which reports I/O with these parameters 10 seconds long and refreshes every second.
I recommend reading the manpage for this tool, as it is quite extensive.
Sometimes the "vmstat" command is also interesting. This will report how much memory is cached by the system / Squid.
By the way, which Linux distribution do you use?
The RPM file for Red Hat Linux 9 is called "sysstat-4.0.7-3.i386.rpm".
You can check if it's installed with the command "rpm -qi sysstat".
If you use a Red Hat distribution, you may want to check out which services are active in which runlevel, you can use the command "chkconfig --list |more".
You can find the homepage of the author of the Linux implementation of 'sar' here : "http://perso.wanadoo.fr/sebastien.godard/"