Using system monitor

My system monitor indicates that Kernel usage (CPU ) is always at 100% even if I close all applications and programs except for monitor and explorer. I can only get down to 75% usage. I am running a Dell Pent II 333 with 256 MB RAM and a 20 GB hard drive. My resource mgr says all three are well over 90% free. My system is slow on start up but after that it seems fine, no error messages. Should I be concerned?