What do you mean by server load?
Do you mean the processor load average (the average number of processes waiting on the processor over a certain time period)? A: On a linux box use w at the command line.
Do you mean the average number of http requests over a certain time period? I'd analize the http logs but I'm sure there's an easier way.
What do you need the server load for? If it's just to show your users how popular your site is I'd show http requests. If it's for load balancing accross multiple web-servers then I'd use the processor load average.
