track cpu usage

[Jack]

Hi,

There is one thing bother me recently:  periodically,  randomly, the cpu
usage reaches 90%+,  then it lasts for 1 or 2 seconds,  during that
period there is no reaction in xterm and anything else(mouse may move
slowly).  

Is there any tool to help me to log all process using over 80% cpu?  

  my system { 
              sid, 2.4.15-aa1, updated & upgraded, 
              PIII 933, 512M, 32M TNT2 with NVdriver 
            }

  processes always on {
              WindowMaker and a bunch of applets,
              galeon,
              mutt,
              a bunch of xterm
            }

Thanks
Jack